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/vegas_mode/coordinator.py

@@ -83,6 +83,8 @@ class VegasModeCoordinator:
 
     # Class-level so coordinators built without __init__ (tests) have it.
     _last_live_check: float = float('-inf')
+    # Set only while Vegas has changed the GIL switch interval; read with getattr.
+    _saved_switch_interval: Optional[float]
 
     def __init__(
         self,
@@ -331,7 +333,7 @@ class VegasModeCoordinator:
             self._saved_switch_interval = sys.getswitchinterval()
         sys.setswitchinterval(ms / 1000.0)
         logger.info("Vegas: GIL switch interval %.1fms (was %.1fms)",
-                    ms, self._saved_switch_interval * 1000.0)
+                    ms, self._saved_switch_interval * 1000.0)  # type: ignore[operator]  # set just above; getattr hides it
 
     def _restore_switch_interval(self) -> None:
         saved = getattr(self, '_saved_switch_interval', None)
@@ -842,7 +844,7 @@ class VegasModeCoordinator:
         plugin_id = self.render_pipeline.next_static_trigger()
         if not plugin_id:
             return None
-        plugin = self.plugin_manager.get_plugin(plugin_id)
+        plugin: Optional['BasePlugin'] = self.plugin_manager.get_plugin(plugin_id)
         if not plugin:
             logger.debug("[%s] STATIC turn reached, but the plugin is no longer loaded",
                          plugin_id)