Release v6.2.5

This is a patch release that improves cache iterators and fixes LRUCache iteration safety, with a small dependency bump and README updates.

Changes

• #74: Iterators returned by keys(), values(), items(), and related views now support len() and bool().
  They report how many items are still left to yield (for TTLCache / VTTLCache, expired entries are skipped). Typing stubs document this as CacheIterator.
• #76: LRUCache now bumps the generation version when a read promotes an entry (moves it to most-recently-used).
  Previously a hit could reorder the list without invalidating live iterators, so concurrent iteration during promotion was not detected correctly. Hits that do not move the entry (already MRU) still skip the bump.
• PyO3 updated from 0.29.1 to 0.29.2.
• #72: README updates and cleanup.

Special Thanks To

• @Malkiz223 for #74 and #76
• @chirizxc for #72

Full Changelog: v6.2.4...v6.2.5