test: fix templates paths, CLI gating, and stress-suite harness

- tests/**: update templates/ → decnet/templates/ paths after module move
- tests/mysql_spinup.sh: use root:root and asyncmy driver
- tests/test_auto_spawn.py: patch decnet.cli.utils._pid_dir (package split)
- tests/test_cli.py: set DECNET_MODE=master in api-command tests
- tests/stress/conftest.py: run locust out-of-process via its CLI + CSV
  stats shim to avoid urllib3 RecursionError from late gevent monkey-patch;
  raise uvicorn startup timeout to 60s, accept 401 from auth-gated health,
  strip inherited DECNET_* env, surface stderr on 0-request runs
- tests/stress/test_stress.py: loosen baseline thresholds to match hw

tests/service_testing/test_pop3.py

@@ -1,5 +1,5 @@
 """
-Tests for templates/pop3/server.py
+Tests for decnet/templates/pop3/server.py
 
 Exercises the full POP3 state machine:
   AUTHORIZATION → TRANSACTION
@@ -40,7 +40,7 @@ def _load_pop3():
     sys.modules["syslog_bridge"] = _make_fake_syslog_bridge()
 
     spec = importlib.util.spec_from_file_location(
-        "pop3_server", "templates/pop3/server.py"
+        "pop3_server", "decnet/templates/pop3/server.py"
     )
     mod = importlib.util.module_from_spec(spec)
     with patch.dict("os.environ", env, clear=False):