Adding GCS support for LRUCache

[ayaka14732]

This PR is a follow-up of #21394, adding GCS support for LRUCache.

Currently, there is existing code in JAX that utilizes etils[epath] to support GCS, falling back to pathlib.Path if etils[epath] is not installed. This PR utilizes the same approach.

Blocking issues:

• TypeError: int() argument must be a string, a bytes-like object or a real number, not 'datetime.datetime' google/etils#621
• epath.Path.touch() does not update mtime google/etils#629
• Return value format of epath.Path.stat() does not match pathlib.Path.stat() google/etils#630

[ayaka14732]

Superseded by #22253