Support `--cache` option in codegen

[mizdra]

[mizdra]

#418 uses a cache to skip only the emit phase. However, ideally, I’d like to skip the check and parse phases as well. Achieving that would require a lot of code changes.

Incidentally, we plan to add support for tsgo to the CSS Modules Kit in the future. Implementing that will require significant code changes. I believe it would be easier to proceed if we tackle the --cache implementation after we’ve finished adding support for tsgo.

Therefore, this effort will be put on hold until the CSS Modules Kit supports tsgo.