Release 24.6.0

[ncoghlan]

• Updated type hints for nullcontext

[ncoghlan]

At this point, there won't be a 21.7.0, we'll be jumping to a 24.x.0 with a newer base contextlib version.

[ncoghlan]

This may end up depending on jazzband/help#364 (depending on whether or not Seth thinks contextlib2 would make a good guinea pig)

[trim21]

there has been 3 years since last release, is there any plan for a new release?