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/cache/memory_cache.py

@@ -8,7 +8,7 @@ import os
 import time
 import threading
 import logging
-from typing import Dict, Any, Optional
+from typing import Dict, Any, Optional, Union
 
 # Historical fixed ceiling, kept as the fallback when RAM cannot be read.
 DEFAULT_MAX_SIZE = 1000
@@ -70,13 +70,15 @@ class MemoryCache:
         """
         self.logger = logging.getLogger(__name__)
         self._cache: Dict[str, Dict[str, Any]] = {}
-        self._timestamps: Dict[str, float] = {}
+        # Values are time.time() floats; get()/cleanup also accept a numeric
+        # string, as a timestamp may have been restored from serialized data.
+        self._timestamps: Dict[str, Union[float, str]] = {}
         self._lock = threading.Lock()
         self._max_size = max_size
         self._cleanup_interval = cleanup_interval
         self._last_cleanup = time.time()
     
-    def get(self, key: str, max_age: Optional[int] = None) -> Optional[Dict[str, Any]]:
+    def get(self, key: str, max_age: Optional[float] = None) -> Optional[Dict[str, Any]]:
         """
         Get value from memory cache.
         
@@ -200,6 +202,7 @@ class MemoryCache:
             max_age_for_cleanup = 3600  # 1 hour
             
             expired_keys = []
+            timestamp: Optional[Union[float, str]]
             for key, timestamp in list(self._timestamps.items()):
                 if isinstance(timestamp, str):
                     try: