fix: handle KeyError in LRUTrieCache move_to_end method

- Added error handling for KeyError when moving items to the end of the LRU cache.
- If the key is not found, it initializes the key with None and then moves it to the end, followed by eviction of the least recently used item.

Author: bradhilton

src/art/tinker/prefix_cache.py

@@ -41,7 +41,12 @@ def lookup(self, rendered_tokens: Sequence[int]) -> PrefixEntry | None:
         if match is None:
             return None
         match_key, entry = match
-        self._lru.move_to_end(match_key)
+        try:
+            self._lru.move_to_end(match_key)
+        except KeyError:
+            self._lru[match_key] = None
+            self._lru.move_to_end(match_key)
+            self._evict()
         return entry
 
     def insert(self, rendered_prefix: Sequence[int], raw_prefix: Sequence[int]) -> None: