Fine-grained ignore rules

[LiamPattinson]

It should be possible to ignore rules on a per-file and per-line basis.

• To ignore rules per file, will need to add project-wide settings file first (Project-wide settings #5). It will be easier to handle this via a settings file or the command line than to parse comments in the files themselves.
• Per-line ignores could be done the same way as flake8/ruff: search for a comment ! noqa at the end of a line. The regex !\w*noqa\w*$ should do it.
  • After gathering rule violations for a file, check the returned line numbers, and search for ! noqa on those lines. Discard violations wherever it's found.
  • Could also have fine-grained ignores, such as ! ignore: E123.
  • Things will get trickier if we also aim to account for line continuations with &.