fix: Adjust OL utils for AF3.1 changes

[kacpermuda]

Airflow 3.1 is changing how the check on EmptyOperators is made when deciding whether or not to schedule them. This PR adjusts OL logic for that to match. I also proposed extracting this decision making into a separate method, so that the listener can simply call it instead of re-creating the logic (#56039).

I'm also hardening the timetable_summary on the DagInfo, when explicit timetable_summary property is missing on Dag model, we can use timetable.summary. For AF 3.1 this property was not present, I added it on time so that there is no change in OL behavior, but we should harden it anyway for future.

---

^ Add meaningful description above
Read the Pull Request Guidelines for more information.
In case of fundamental code changes, an Airflow Improvement Proposal (AIP) is needed.
In case of a new dependency, check compliance with the ASF 3rd Party License Policy.
In case of backwards incompatible changes please leave a note in a newsfragment file, named {pr_number}.significant.rst or {issue_number}.significant.rst, in airflow-core/newsfragments.

[kacpermuda]

Airflow 3.1 is changing how the check on EmptyOperators is made when deciding whether or not to schedule them. This PR adjusts OL logic for that to match. I also proposed extracting this decision making into a separate method, so that the listener can simply call it instead of re-creating the logic (#56039).

I'm also hardening the timetable_summary on the DagInfo, when explicit timetable_summary property is missing on Dag model, we can use timetable.summary. For AF 3.1 this property was not present, I added it on time so that there is no change in OL behavior, but we should harden it anyway for future.

---

^ Add meaningful description above
Read the Pull Request Guidelines for more information.
In case of fundamental code changes, an Airflow Improvement Proposal (AIP) is needed.
In case of a new dependency, check compliance with the ASF 3rd Party License Policy.
In case of backwards incompatible changes please leave a note in a newsfragment file, named {pr_number}.significant.rst or {issue_number}.significant.rst, in airflow-core/newsfragments.

[kacpermuda]

Airflow 3.1 is changing how the check on EmptyOperators is made when deciding whether or not to schedule them. This PR adjusts OL logic for that to match. I also proposed extracting this decision making into a separate method, so that the listener can simply call it instead of re-creating the logic (#56039).

I'm also hardening the timetable_summary on the DagInfo, when explicit timetable_summary property is missing on Dag model, we can use timetable.summary. For AF 3.1 this property was not present, I added it on time so that there is no change in OL behavior, but we should harden it anyway for future.

---

^ Add meaningful description above
Read the Pull Request Guidelines for more information.
In case of fundamental code changes, an Airflow Improvement Proposal (AIP) is needed.
In case of a new dependency, check compliance with the ASF 3rd Party License Policy.
In case of backwards incompatible changes please leave a note in a newsfragment file, named {pr_number}.significant.rst or {issue_number}.significant.rst, in airflow-core/newsfragments.

[kacpermuda]

Airflow 3.1 is changing how the check on EmptyOperators is made when deciding whether or not to schedule them. This PR adjusts OL logic for that to match. I also proposed extracting this decision making into a separate method, so that the listener can simply call it instead of re-creating the logic (#56039).

I'm also hardening the timetable_summary on the DagInfo, when explicit timetable_summary property is missing on Dag model, we can use timetable.summary. For AF 3.1 this property was not present, I added it on time so that there is no change in OL behavior, but we should harden it anyway for future.

---

^ Add meaningful description above
Read the Pull Request Guidelines for more information.
In case of fundamental code changes, an Airflow Improvement Proposal (AIP) is needed.
In case of a new dependency, check compliance with the ASF 3rd Party License Policy.
In case of backwards incompatible changes please leave a note in a newsfragment file, named {pr_number}.significant.rst or {issue_number}.significant.rst, in airflow-core/newsfragments.

[kacpermuda]

Airflow 3.1 is changing how the check on EmptyOperators is made when deciding whether or not to schedule them. This PR adjusts OL logic for that to match. I also proposed extracting this decision making into a separate method, so that the listener can simply call it instead of re-creating the logic (#56039).

I'm also hardening the timetable_summary on the DagInfo, when explicit timetable_summary property is missing on Dag model, we can use timetable.summary. For AF 3.1 this property was not present, I added it on time so that there is no change in OL behavior, but we should harden it anyway for future.

---

^ Add meaningful description above
Read the Pull Request Guidelines for more information.
In case of fundamental code changes, an Airflow Improvement Proposal (AIP) is needed.
In case of a new dependency, check compliance with the ASF 3rd Party License Policy.
In case of backwards incompatible changes please leave a note in a newsfragment file, named {pr_number}.significant.rst or {issue_number}.significant.rst, in airflow-core/newsfragments.

[kacpermuda]

Airflow 3.1 is changing how the check on EmptyOperators is made when deciding whether or not to schedule them. This PR adjusts OL logic for that to match. I also proposed extracting this decision making into a separate method, so that the listener can simply call it instead of re-creating the logic (#56039).

I'm also hardening the timetable_summary on the DagInfo, when explicit timetable_summary property is missing on Dag model, we can use timetable.summary. For AF 3.1 this property was not present, I added it on time so that there is no change in OL behavior, but we should harden it anyway for future.

---

^ Add meaningful description above
Read the Pull Request Guidelines for more information.
In case of fundamental code changes, an Airflow Improvement Proposal (AIP) is needed.
In case of a new dependency, check compliance with the ASF 3rd Party License Policy.
In case of backwards incompatible changes please leave a note in a newsfragment file, named {pr_number}.significant.rst or {issue_number}.significant.rst, in airflow-core/newsfragments.

[kacpermuda]

Airflow 3.1 is changing how the check on EmptyOperators is made when deciding whether or not to schedule them. This PR adjusts OL logic for that to match. I also proposed extracting this decision making into a separate method, so that the listener can simply call it instead of re-creating the logic (#56039).

I'm also hardening the timetable_summary on the DagInfo, when explicit timetable_summary property is missing on Dag model, we can use timetable.summary. For AF 3.1 this property was not present, I added it on time so that there is no change in OL behavior, but we should harden it anyway for future.

---

^ Add meaningful description above
Read the Pull Request Guidelines for more information.
In case of fundamental code changes, an Airflow Improvement Proposal (AIP) is needed.
In case of a new dependency, check compliance with the ASF 3rd Party License Policy.
In case of backwards incompatible changes please leave a note in a newsfragment file, named {pr_number}.significant.rst or {issue_number}.significant.rst, in airflow-core/newsfragments.

[kacpermuda]

Airflow 3.1 is changing how the check on EmptyOperators is made when deciding whether or not to schedule them. This PR adjusts OL logic for that to match. I also proposed extracting this decision making into a separate method, so that the listener can simply call it instead of re-creating the logic (#56039).

I'm also hardening the timetable_summary on the DagInfo, when explicit timetable_summary property is missing on Dag model, we can use timetable.summary. For AF 3.1 this property was not present, I added it on time so that there is no change in OL behavior, but we should harden it anyway for future.

---

^ Add meaningful description above
Read the Pull Request Guidelines for more information.
In case of fundamental code changes, an Airflow Improvement Proposal (AIP) is needed.
In case of a new dependency, check compliance with the ASF 3rd Party License Policy.
In case of backwards incompatible changes please leave a note in a newsfragment file, named {pr_number}.significant.rst or {issue_number}.significant.rst, in airflow-core/newsfragments.