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/exceptions.py

@@ -5,11 +5,13 @@ Provides specific exception types for different error categories,
 enabling better error handling and debugging.
 """
 
+from typing import Optional
+
 
 class LEDMatrixError(Exception):
     """Base exception for all LEDMatrix errors."""
     
-    def __init__(self, message: str, context: dict = None):
+    def __init__(self, message: str, context: Optional[dict] = None):
         """
         Initialize the exception.
         
@@ -32,7 +34,7 @@ class LEDMatrixError(Exception):
 class CacheError(LEDMatrixError):
     """Exception raised for cache-related errors."""
     
-    def __init__(self, message: str, cache_key: str = None, context: dict = None):
+    def __init__(self, message: str, cache_key: Optional[str] = None, context: Optional[dict] = None):
         """
         Initialize cache error.
         
@@ -53,7 +55,7 @@ class CacheError(LEDMatrixError):
 class ConfigError(LEDMatrixError):
     """Exception raised for configuration-related errors."""
     
-    def __init__(self, message: str, config_path: str = None, field: str = None, context: dict = None):
+    def __init__(self, message: str, config_path: Optional[str] = None, field: Optional[str] = None, context: Optional[dict] = None):
         """
         Initialize config error.
         
@@ -79,7 +81,7 @@ class ConfigError(LEDMatrixError):
 class PluginError(LEDMatrixError):
     """Exception raised for plugin-related errors."""
     
-    def __init__(self, message: str, plugin_id: str = None, context: dict = None):
+    def __init__(self, message: str, plugin_id: Optional[str] = None, context: Optional[dict] = None):
         """
         Initialize plugin error.
         
@@ -100,7 +102,7 @@ class PluginError(LEDMatrixError):
 class DisplayError(LEDMatrixError):
     """Exception raised for display-related errors."""
     
-    def __init__(self, message: str, display_mode: str = None, context: dict = None):
+    def __init__(self, message: str, display_mode: Optional[str] = None, context: Optional[dict] = None):
         """
         Initialize display error.