Docs: Fix TextCalendar.formatweek() and formatmonthname() signatures - #159516

The documented signatures of TextCalendar.formatweek() and TextCalendar.formatmonthname() don't match the code. In both methods width is a required argument:

def formatweek(self, theweek, width): ...
def formatmonthname(self, theyear, themonth, width, withyear=True): ...

The docs show formatweek(theweek, w=0) and formatmonthname(theyear, themonth, width=0, withyear=True). If you follow them, you get errors:

>>> import calendar
>>> c = calendar.TextCalendar()
>>> week = c.monthdays2calendar(2026, 10)[0]
>>> c.formatweek(week)
TypeError: TextCalendar.formatweek() missing 1 required positional argument: 'width'
>>> c.formatweek(week, w=3)
TypeError: TextCalendar.formatweek() got an unexpected keyword argument 'w'
>>> c.formatmonthname(2026, 10)
TypeError: TextCalendar.formatmonthname() missing 1 required positional argument: 'width'

This PR changes the two signatures to match the code and rewords the formatweek() description to use width. It only touches the docs, so I think it needs the "skip news" label.