* Fix BaseFileCacheModule#keys to respect prefix
Change:
- Previously BaseFileCacheModule#keys would return keys with the cache
prefix. These keys are impossible to retrieve from the cache without
removing the prefix or using the cache without a prefix.
Now it removes the prefix from the key and only returns keys that
share the same prefix as the cache.
Test Plan:
- New unit tests
* Add explicit BaseFileCacheModule#keys test
Test that files that do not match the cache prefix are ignored.
Test that the prefix is removed from the cache key.
