Annotate coverage, artifacts and corpus dirs with CACHEDIR.TAG

[totikom]

CACHEDIR.TAG is a widely adopted way to mark directories, that should be excluded from backups, archives and so on.
IMO, coverage, artifacts and corpus directories should not be backed up, so this change is beneficial for setups with automatic backups.

[totikom]

CI is failing because of this two tests:

But on my machine they are also failing on main branch. Can someone verify, if everything is ok with this tests on main?

[Shnatsel]

Artifacts are especially valuable and have very low size (~kilobytes), so I see no reason to exclude them from backups.

I also tend to back up my corpora because they took days of compute to acquire, while only taking up single-digit numbers of megabytes even for large corpora (1000+ files).

If you are looking to reduce the size of backups, a much better way to approach it would be excluding the target directory, which is both reproducible without investing days of compute, and is multiple orders of magnitude larger.

Since this change is not clearly beneficial, and none of the maintainers can dogfood it and notice if something breaks, I'm going to go ahead and close this.