fix(cache): lazy-init TTL cache locks to survive event-loop turnover

A module-level asyncio.Lock binds to the loop it was first awaited on.
Under pytest-anyio (and xdist) each test spins up a new loop; any later
test that hit /health or /config would wait on a lock owned by a dead
loop and the whole worker would hang.

Create the lock on first use and drop it in the test-reset helpers so a
fresh loop always gets a fresh lock.

decnet/web/router/config/api_get_config.py

@@ -24,6 +24,9 @@ _state_locks: dict[str, asyncio.Lock] = {}
 def _reset_state_cache() -> None:
     """Reset cached config state — used by tests."""
     _state_cache.clear()
+    # Drop any locks bound to the previous event loop — reusing one from
+    # a dead loop deadlocks the next test.
+    _state_locks.clear()
 
 
 async def _get_state_cached(name: str) -> Optional[dict[str, Any]]: