refactor: clean up inference design patterns

1. KVCache base: add default task_cached/task_record_hashes, remove getattr from scheduler
2. Remove page_size param from scheduler constructor (ContiguousCache-only)
3. InferenceEngine expose cache param for KVCache injection
4. Rename page_cache -> kv_cache in Executor
5. Move stream_callback from Task to TaskManager._callbacks dict
6. TaskManager.clear_queues clears callbacks

astrai/inference/core/cache.py

@@ -303,6 +303,13 @@ class KVCache(ABC):
         self, task_ids: List[str], total_len: int, device: torch.device
     ) -> CacheView: ...
 
+    def task_cached(self, task_id: str) -> int:
+        return 0
+
+    def task_record_hashes(
+        self, task_id: str, prompt_ids: List[int], start_logical_page: int = 0
+    ): ...
+
 
 class PageCacheView(CacheView):
     """Bundles Storage + page_table + total_len for attention layers."""