ci: mypy ratchet -- keep type-clean modules clean (71 modules, 536 -> 442 errors) (#661)

* ci: mypy ratchet -- keep type-clean modules clean

mypy-clean.txt lists the 71 modules under src/ that type-check clean;
scripts/check_types.py runs mypy (--follow-imports=silent) on exactly
those files and fails on any error or a missing/unsorted/duplicate entry.
A new "Type check (mypy ratchet)" CI job runs it with mypy 1.20.2 and
pinned stubs; the manual pre-commit mypy hook now runs the same script
(a local hook, so mypy sees the installed requirements like CI does).

35 modules were made clean with annotation-only fixes: hints, typing.cast,
TYPE_CHECKING imports, implicit-Optional defaults made explicit, and
annotations widened (never guards removed) where mypy called a defensive
isinstance check unreachable. No runtime behaviour change.

mypy.ini: numpy and orjson are treated as Any (follow_imports=skip, also
for stubs). numpy 2.3+ stubs use 3.12 `type` statements that mypy won't
parse at python_version 3.10, and orjson is optional, so seeing its stubs
made the result depend on whether it was installed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* chore: annotate check_types.py's list-form mypy subprocess

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

src/common/frame_timing.py

@@ -93,7 +93,7 @@ import tempfile
 import threading
 import time
 import traceback
-from typing import Any, Callable, Dict, List, Optional, Tuple
+from typing import Any, Callable, Dict, List, Optional, Tuple, TypedDict
 
 logger = logging.getLogger(__name__)
 
@@ -483,7 +483,13 @@ class FrameTimingRecorder:
             raise
 
 
-def watchdog_settings() -> Dict[str, float]:
+class _WatchdogSettings(TypedDict, total=False):
+    """The StallWatchdog keyword arguments watchdog_settings() may set."""
+    threshold: float
+    poll: float
+
+
+def watchdog_settings() -> _WatchdogSettings:
     """StallWatchdog arguments from ``LEDMATRIX_STALL_WATCHDOG_MS``, if set.
 
     The poll comes down with the threshold, or a stall shorter than one poll