Highlight today in colour in calendar's CLI output

[hugovk]

Feature or enhancement

In Python 3.13 we added colour output to the new REPL, tracebacks and doctest, and in 3.14 to unittest and test.regrtest, which can also be controlled with the PYTHON_COLORS, NO_COLOR and FORCE_COLOR environment variables:

• https://docs.python.org/3.14/whatsnew/3.14.html#unittest
• https://docs.python.org/3.14/using/cmdline.html#using-on-controlling-color

On macOS, the cal utility does something similar, but highlights today.

The calendar module has a CLI to print out a calendar to the terminal, but with no highlighting. Let's add it.

Linked PRs

• gh-128317: Highlight today in colour in calendar CLI output #128318
• gh-128317: Document calendar.TextCalendar.formatweek #128353
• [3.13] gh-128317: Document calendar.TextCalendar.formatweek (GH-128353) #128357
• [3.12] gh-128317: Document calendar.TextCalendar.formatweek (GH-128353) #128358
• gh-128317: Move CLI calendar highlighting to private class #129625

[encukou]

Thank you!
I hate to spoil the fun, but this breaks non-interactive usage (e.g. ./python -m calendar | less).
IMO, the default should look at sys.stdout.isatty() (not stderr). , and be off for formatweek (edit: oh, it already is).