Closes #2

No-response messages need to be configured through Negotiate messages
passed between the MTA and filter.

This is specifically for Flakeheaven's cache, which does not (yet)
include automatic .gitignore

Closes #8

… and use them to fix message typing in test/example_filter.py

Closes #6

Fixes #1

This is to make installing the dependencies easier for developers,
although unfortunately it leaks into the released packages in the form
of an optional dependency group.

Closes #5

The hook doesn't support module attribute docstrings and never will
apparently:

https://github.com/pre-commit/pre-commit-hooks/issues/159
https://github.com/pre-commit/pre-commit-hooks/pull/812

Fixes #4