Vecstream

Fixed
- Fixed metadata filtering in HNSW search by increasing the number of candidates to ensure enough matches are found after filtering
- Ensure search_similar method properly limits results to k items
- Fixed import error by renaming VectorDBClient to ClientAPI
- Updated GitHub workflows to only test with Python 3.12

Added
- Initial release with core vector database functionality
- HNSW indexing for fast similarity search
- Collections/namespaces for organizing vectors
- Metadata filtering support
- Binary persistence layer
- CLI interface for basic operations