Add "module" post-write hook

Add "module" post-write hook

This hook type is almost identical to the console_scripts hook, except
it's running `python -m black` instead of using black's console_script.

It is mainly useful for tools without console scripts (e.g. ruff), but
has semantics closer to the console_scripts hook in that it finds the
ruff module available to the running interpreter instead of finding
an executable by path.

Fixes #1686