Cache state consistency

Ensure cache operations maintain consistent state and handle shared resources properly throughout the cache lifecycle. This includes proper key type management, safe eviction of shared entries, and accurate state tracking across different operational phases.

Key practices:

1. Type-safe cache keys: Always use proper key types rather than strings to prevent cache misses due to type mismatches
2. Reference-aware eviction: Check reference counts before evicting cache entries that may be shared between multiple requests
3. Consistent state tracking: Maintain accurate phase detection and state information to prevent incorrect cache behavior

Example of proper reference checking before eviction:

# Check ref_count before evicting shared cache entries
if self.memory_allocator.get_ref_count(self.hot_cache[evict_key]) > 1:
    continue  # Skip eviction if still referenced

Example of proper key type handling:

# Convert string keys to proper types before cache operations
for idx, key_str in enumerate(alloc_request.keys):
    key = CacheEngineKey.from_string(key_str)  # Ensure proper type
    if self._backend.contains(key, pin=True):  # Now works correctly

This prevents cache leaks, ensures proper cache hits, and maintains system reliability when cache entries are shared across multiple operations or requests.