refactor(proto): remove legacy scan field

[Phoenix500526]

Which issue does this PR close?

• Closes #N/A.

Rationale for this change

Since DataFusion doesn't typically guartantee wire format compatibility, I remove the backward compatiblity shim that introduced in PR #23189

FYI: #23189 (comment)

What changes are included in this PR?

DataFusion does not guarantee serialized plans across versions. Keeping partitioned_by_file_group therefore leaves a dead schema field and decoder path after output_partitioning became the source of truth. Reserve the old field number and name to prevent future reuse.

Are these changes tested?

Yes

Are there any user-facing changes?

Yes

[github-actions]

Thank you for opening this pull request!

Reviewer note: cargo-semver-checks reported the current version number is not SemVer-compatible with the changes in this pull request (compared against the base branch).

Details

 Cloning apache/main
Building datafusion-proto v54.1.0 (current)
Built [ 59.664s] (current)
Parsing datafusion-proto v54.1.0 (current)
Parsed [ 0.019s] (current)
Building datafusion-proto v54.1.0 (baseline)
Built [ 59.083s] (baseline)
Parsing datafusion-proto v54.1.0 (baseline)
Parsed [ 0.020s] (baseline)
Checking datafusion-proto v54.1.0 -> v54.1.0 (no change; assume patch)
Checked [ 0.259s] 223 checks: 223 pass, 30 skip
Summary no semver update required
Finished [ 120.371s] datafusion-proto
Building datafusion-proto-models v54.1.0 (current)
Built [ 24.590s] (current)
Parsing datafusion-proto-models v54.1.0 (current)
Parsed [ 0.129s] (current)
Building datafusion-proto-models v54.1.0 (baseline)
Built [ 24.358s] (baseline)
Parsing datafusion-proto-models v54.1.0 (baseline)
Parsed [ 0.130s] (baseline)
Checking datafusion-proto-models v54.1.0 -> v54.1.0 (no change; assume patch)
Checked [ 1.751s] 223 checks: 221 pass, 2 fail, 0 warn, 30 skip
--- failure inherent_method_missing: pub method removed or renamed ---
Description:
A publicly-visible method or associated fn is no longer available under its prior name. It may have been renamed or removed entirely.
ref: https://doc.rust-lang.org/cargo/reference/semver.html#item-remove
impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.49.0/src/lints/inherent_method_missing.ron
Failed in:
FileScanExecConf::partitioned_by_file_group, previously in file /home/runner/work/datafusion/datafusion/target/semver-checks/git-apache_main/aaddf2eed7ce0cd70ec49304db33795fd8ddd9b1/datafusion/proto-models/src/generated/prost.rs:1854
FileScanExecConf::partitioned_by_file_group, previously in file /home/runner/work/datafusion/datafusion/target/semver-checks/git-apache_main/aaddf2eed7ce0cd70ec49304db33795fd8ddd9b1/datafusion/proto-models/src/generated/prost.rs:1854
--- failure struct_pub_field_missing: pub struct's pub field removed or renamed ---
Description:
A publicly-visible struct has at least one public field that is no longer available under its prior name. It may have been renamed or removed entirely.
ref: https://doc.rust-lang.org/cargo/reference/semver.html#item-remove
impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.49.0/src/lints/struct_pub_field_missing.ron
Failed in:
field partitioned_by_file_group of struct FileScanExecConf, previously in file /home/runner/work/datafusion/datafusion/target/semver-checks/git-apache_main/aaddf2eed7ce0cd70ec49304db33795fd8ddd9b1/datafusion/proto-models/src/generated/prost.rs:1879
field partitioned_by_file_group of struct FileScanExecConf, previously in file /home/runner/work/datafusion/datafusion/target/semver-checks/git-apache_main/aaddf2eed7ce0cd70ec49304db33795fd8ddd9b1/datafusion/proto-models/src/generated/prost.rs:1879
Summary semver requires new major version: 2 major and 0 minor checks failed
Finished [ 52.026s] datafusion-proto-models

[Phoenix500526]

Hi @alamb , sorry to ping. Could you take a look at this PR when you have time?

This removes the legacy scan field from the proto as you mentioned in
#23189 (comment), and I would appreciate any guidance if you think the direction should change.

Thanks.

[alamb]

Thank you for the followup @Phoenix500526

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.65%. Comparing base (88365dd) to head (fee179f).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@ Coverage Diff @@## main #23445 +/- ##
==========================================
- Coverage 80.65% 80.65% -0.01% 
==========================================
Files 1093 1093 Lines 371619 371596 -23 Branches 371619 371596 -23 ==========================================
- Hits 299730 299705 -25 
Misses 53993 53993 - Partials 17896 17898 +2 

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