Datetime: Tidy up docs

[StanFromIreland]

Fix some style guide infringements (case of titles, Latin abbreviations), add parameter mark up in a few places, fix a small typo, make spacing of docs consistent, and add an inheritance diagram (like pathlib's :-).

Diagram

Generated with graphviz, and:

digraph {
graph [
bgcolor="transparent"
fontnames = "svg"
layout="dot"ranksep=0.5
nodesep=0.5
splines=line
]
node [
fontname="Courier"fontsize=14.0
shape=boxstyle=rounded
margin="0.15,0.07"
]
edge [
arrowhead=none
]
object -> tzinfo
object -> timedelta
object -> time
object -> date
tzinfo -> timezone
date -> datetime
}

---

📚 Documentation preview 📚: https://cpython-previews--144720.org.readthedocs.build/en/144720/library/datetime.html

[AA-Turner]

The diagram in pathlib is useful as the inheritance is non-standard. I don't think that's the case here, perhaps the only such instance is date <- datetime. What's the justification for adding it?

[StanFromIreland]

What's the justification for adding it?

The diagram is already in the documentation, albeit in textual form.

[AA-Turner]

feedback: this PR could have been more usefully structured as an optional set of style guide changes, addition of markup, and adding an image; to allow discussing each on its own merits.

Probably not worth doing now that this has been opened, but please keep in mind for the future.

A

[StanFromIreland]

Thanks Hugo!

[miss-islington-app]

Thanks @StanFromIreland for the PR, and @encukou for merging it 🌮🎉.. I'm working now to backport this PR to: 3.14.
🐍🍒⛏🤖

[miss-islington-app]

Sorry, @StanFromIreland and @encukou, I could not cleanly backport this to 3.14 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker c6a142f9472f2d3e2c360b72a19450f9dd087657 3.14

[bedevere-app]

GH-144956 is a backport of this pull request to the 3.14 branch.