This package is a copy of cmd/go/internal/cache.

Differences from upstream:
- we continue to use renameio instead of lockedfile for writing trim.txt
- we still use I/O helpers that work with earlier versions of Go.
- we use a cache directory specific to Staticcheck
- we use a Staticcheck-specific salt

The last upstream commit we've looked at was:
06ac303f6a14b133254f757e54599c48e3c2a4ad
