Previously, the ecosystem checks formatted with the baseline then
formatted again with `--diff` to get the changed files.

Now, the ecosystem checks support a new mode where we:
- Format with the baseline
- Commit the changes
- Reset to the target ref
- Format again
- Check the diff from the baseline commit

This effectively tests Ruff changes on unformatted code rather than
changes in previously formatted code (unless, of course, the project is
already using Ruff).

While this mode is the new default, I've retained the old one for local
checks. The mode can be toggled with `--format-comparison <type>`.

Includes some more aggressive resetting of the GitHub repositories when
cached.

Here, I've also stubbed comparison modes in which `black` is used as the
baseline. While these do nothing here, #8419 adds support.

I tested this with the commit from #8216 and ecosystem changes appear
https://gist.github.com/zanieb/a982ec8c392939043613267474471a6e