gh-140715: Add %t and %n format codes support to strptime()

[jyalim]

Incrementally builds C99+ datetime support with addition of %t and %n with two lines of code. Also adds tests and updates documentation.

Continued effort from PR: #140647 , #144819.

Documentation drops (0) footnote.

Passed all tests.

Passed patchcheck.

Issue: #140715

• Issue: Update str*time to C11 format codes #140715

Note, this PR originally only was for %t; %n was added 2026-02-25.

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📚 Documentation preview 📚: https://cpython-previews--144896.org.readthedocs.build/

[StanFromIreland]

This is quite an odd case, as per the standard for strftime, it is a \t character, however, for strptime():

A series of conversion specifications composed of %n, %t, white-space bytes, or any combination is executed by scanning up to the first non-white-space byte (which remains unscanned), or until no more characters can be scanned.

And, more straightforward:

Arbitrary whitespace.

Considering that this is the wide-spread behaviour, it should instead be r'\s+' for %n/%t (with additional tests), and add a note to the doc.

[jyalim]

Thanks, this was a great catch that adds some power to %t for strptime. I've implemented the changes!

[jyalim]

Thank you, the documentation changes were implemented.

[StanFromIreland]

We could also do \n now, since it is equivalent. (re-use the tests please)

[jyalim]

Thanks! All the requested changes were implemented. The title and description of this PR were also updated to include %n.

[jyalim]

Thank you, the tests have been merged and all requested changes have been implemented.

[StanFromIreland]

Something broke with the CI, I'll try updating the branch.

[jyalim]

Thanks! Changes have been made.