Based on the repository's commit message style and the changes in the diff, here's an appropriate commit message:

```
feat: add websocket tests, PoA metrics, marketplace endpoints, and enhanced observability

- Add comprehensive websocket tests for blocks and transactions streams including multi-subscriber and high-volume scenarios
- Extend PoA consensus with per-proposer block metrics and rotation tracking
- Add latest block interval gauge and RPC error spike alerting
- Enhance mock coordinator

apps/blockchain-node/tests/conftest.py

@@ -1,8 +1,15 @@
 from __future__ import annotations
 
+import sys
+from pathlib import Path
+
 import pytest
 from sqlmodel import SQLModel, Session, create_engine
 
+PROJECT_ROOT = Path(__file__).resolve().parent.parent / "src"
+if str(PROJECT_ROOT) not in sys.path:
+    sys.path.insert(0, str(PROJECT_ROOT))
+
 from aitbc_chain.models import Block, Transaction, Receipt  # noqa: F401 - ensure models imported for metadata