BUG: Add AM/PM token support on guess_datetime_format

[juli4nb4dillo]

• closes BUG: to_datetime ignores "AM" and "PM" unless format is explicitly set #53147
• Tests added and passed if fixing a bug or adding a new feature
• All code checks passed.
• Added type annotations to new arguments/methods/functions.
• Added an entry in the latest doc/source/whatsnew/v2.1.0.rst file if fixing a bug or adding a new feature.

[MarcoGorelli]

thanks for your PR - there's some failing tests, could you fix them up please?

[MarcoGorelli]

thanks - will need a whatsnew note for 2.1 too

[MarcoGorelli]

can you keep these in but change the expected fmt (the second argument) to be None?

[juli4nb4dillo]

Okay, let me see if I can setup my env to build and test locally, otherwise I'm kinda flying blind waiting for Github Actions to run

[MarcoGorelli]

you could try gitpod if you're having trouble, else feel free to ask on the slack

[juli4nb4dillo]

Mmm... it guesses the format to be "%a %d %b %Y %H:%M:%S AM" instead of None, which has to do with this loop:

pandas/pandas/_libs/tslibs/parsing.pyx

Lines 1012 to 1018 in 8894dcc

	try:
	# If the token is numeric, then we likely didn't parse it
	# properly, so our guess is wrong
	float(tokens[i])
	return None
	except ValueError:
	pass

Let me try again from the top, I think we can make it work with the "AM/PM" tokens easier now that I can test locally.

[mroeschke]

Is this PR or #53257 supposed to fix this?

[juli4nb4dillo]

@mroeschke It's duplicate, sorry for that, I wanted to test it from the top so I made another branch.
This one is wrong anyway.