feat: add cache flush API and fix cache key consistency

- Add PUT /cache/flush endpoint for selective cache management
- Fix critical cache key mismatch in cleanup_expired_index()
- Update index file detection to use full path instead of filename
- Bump version to 2.0.2

The key changes include adding a comprehensive cache flush API that supports selective flushing by cache type (index, files, metrics) and fixing a critical bug where cache keys were
inconsistent between storage and cleanup operations, preventing proper cache invalidation.

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "artifactapi"
-version = "2.0.1"
+version = "2.0.2"
 description = "Generic artifact caching system with support for various package managers"
 
 dependencies = [