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/display_manager.py

@@ -51,13 +51,16 @@ from src.pi5_matrix_support import is_raspberry_pi_5
 import threading
 import time
 from collections import OrderedDict, deque
-from typing import Dict, Any, List, Optional, Tuple
+from typing import Dict, Any, List, Optional, Tuple, TYPE_CHECKING
 import math
 import zlib
 import freetype
 
 from src.common import snapshot_policy
 from src.common.frame_timing import FrameTimingRecorder
+
+if TYPE_CHECKING:
+    from src.common.render_gate import RenderGate
 from src.deprecation import deprecated
 from src.logging_config import get_logger
 from src.common.permission_utils import (
@@ -341,7 +344,7 @@ class DisplayManager:
         # A src.common.render_gate.RenderGate while Vegas runs with
         # vegas_scroll.prefetch_gate on: opened around each swap so the
         # prefetch thread only runs Python while this thread waits on vsync.
-        self.render_gate = None
+        self.render_gate: Optional['RenderGate'] = None
 
         # Timing of every presented frame, whoever drew it, for
         # scripts/frame_soak.py. See src/common/frame_timing.py.