fix: Export MemcachedV1KeySanitizationStrategy from memcached store module

The MemcachedV1KeySanitizationStrategy was defined but not exported from the
memcached store's __init__.py, causing import errors in tests and user code.

Co-authored-by: William Easton <strawgate@users.noreply.github.com>

Author: github-actions[bot]

key-value/key-value-aio/src/key_value/aio/stores/memcached/__init__.py

@@ -1,3 +1,3 @@
-from key_value.aio.stores.memcached.store import MemcachedStore
+from key_value.aio.stores.memcached.store import MemcachedStore, MemcachedV1KeySanitizationStrategy
 
-__all__ = ["MemcachedStore"]
+__all__ = ["MemcachedStore", "MemcachedV1KeySanitizationStrategy"]