gh-140212: Add html for year-month option in Calendar

[pgdr]

Running python3.13 -m calendar 2025 pretty-prints the calendar for all of 2025. If we add the month at the end, it only prints the month.

python3.13 -m calendar 2025

It is possible to get HTML output by using python -m calendar -t html 2025, which gives the calender for 2025 in HTML format.

However, if we add the month, python -m calendar -t html 2025 10 it fails:

[~]$ python3.13 -m calendar -t html 2025 10
usage: calendar.py [-h] [-w WIDTH] [-l LINES] [-s SPACING] [-m MONTHS] [-c CSS] [-L LOCALE] [-e ENCODING] [-t {text,html}] [-f FIRST_WEEKDAY]
                   [year] [month]
calendar.py: error: incorrect number of arguments

---

This PR simply adds support for HTML-formatting the year-month option.

A test is included, and one existing test is removed: a test verifying that the year month option fails.

• Issue: Calendar fails to produce html on year and month #140212

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Most changes to Python require a NEWS entry. Add one using the blurb_it web app or the blurb command-line tool.

If this change has little impact on Python users, wait for a maintainer to apply the skip news label instead.

[pgdr]

Note that the html produced in Calendar.formatmonthpage is essentially copied verbatim from Calender.formatyearpage. There is potential for code reuse and extracting common (html) code into a new function.

I didn't do this at this stage because it would actually be a larger change, and I'm not sure this will be merged regardless.

Let me know if I should extract the common code out.

[StanFromIreland]

Please add a blurb and docs.

[pgdr]

@StanFromIreland I have added a blurb and updated documentation for Calendar's argparser.

I was not sure if the blurb was supposed to go in Core_and_Builtins or elsewhere, I will move it to its correct location if it's wrong.

I have updated the docs as well.

I think it's best to squash the commits before a hypothetical merging. I'll do so upon request.

[StanFromIreland]

It should be in Library.

Squash is done by the commiter, please don't force push, it only causes confusion.

[pgdr]

@StanFromIreland I have moved the blurb to Library.

[hugovk]

Please could you also list this in What's New?

https://docs.python.org/3.15/whatsnew/3.15.html#calendar

[pgdr]

@hugovk It's done (given that the entry is acceptable).

[hugovk]

Thank you!

[pgdr]

@AA-Turner Let me know if there is anything I can do at this point to get this PR merged.