custom codemod cli

[onerandomusername]

Is it possible to completely skip parsing of files that don't contain this string? It's not really worth it to parse the module into a CST (certainly the most expensive part of the process), only to skip it based on the original raw text contents.

If not possible with libcst.tool, we might be able to write our own entrypoint that filters files before passing them into libcst, shouldn't be too complex since they provide a couple useful tools: https://libcst.readthedocs.io/en/latest/codemods.html#command-line-toolkit

Alternatively, we could use the nox session to filter them before calling libcst; it would require always using nox instead of calling libcst directly, but that should be fine.

Originally posted by @shiftinv in https://github.com/DisnakeDev/disnake/pull/708#discussion_r947330751