Filecheckize

- Add spacing by default and --compact-output for compatibility (7)
- Comments-related QoL flags (8)
- `--strip-comments` now takes an optional argument to strip comments given a custom comment prefix. (e.g., `--strip-comments ` will strip lines starting by `` from the input). It defaults to `//` for compatibility.
- `--comment-prefix`, which was used for the above functionality, now enables choosing a comment prefix *for the output*

- Add Python 3.12 support.
- Add `--xdsl-anonymize`, similar to `--mlir-anonymize`, but keeping *named* values explicit.
- Update dependencies.

Initial release.