Update `str*time` to C11 format codes

[StanFromIreland]

Feature or enhancement

There are several things to do, these are already supported by strftime but some (support for a few was added recently but not documented) are not supported by strptime (e.g. %t is not supported).

• Update docs, currently the table is a bit messy with non-standard format codes listed, i.e. %f, and quite a few codes are missing.
• Refactor strftime tests, they were written when the format codes were not expected.
• Complete strptime, e.g. %n.
• Consider: Add an entry to What's New

I will be working on this and most likely extending this list.

Linked PRs

• gh-140715: Update datetime.*.str*time format code tables #140716
• gh-140715: provide support for %F token in strptime; add test for it and %T #140647

[AA-Turner]

Note that we don't currently have exact correspondance with the C standard (the second table here), so any new format codes should be treated as new features for Python, rather than a pure conformance bug.

A

[StanFromIreland]

should be treated as new features for Python, rather than a pure conformance bug.

I agree, although also note two entries in the second table are supported in C11 and will be moved to the main table.