The MCP server previously created a new PersistentClient on every tool
call via _get_collection(). This incurs HNSW index loading overhead
on each request.
Cache the client and collection at module level. The cache resets
naturally on process restart (MCP runs as a subprocess).
Also adds a _reset_mcp_cache fixture to conftest.py for test isolation.
Includes test infrastructure from PR #131.
92 tests pass.
Igor Lins e Silva
a67b00d7c7