test(util): cover minimatchFilter and cachePathIsFile gaps
Brings lib/util to 100% coverage:
- minimatchFilter: the closure returned on the uncached path was never
invoked, and the options-based cache key branch was never taken
- cachePathIsFile: only the "does not exist" path was tested, so
stat().isFile() never ran
Co-authored-by: Claude Opus 5 <michael.kriese+claude-code@mend.io>