fix(memory): move Sequence to TYPE_CHECKING block, use hasattr for backend detection

- Import Sequence under TYPE_CHECKING to satisfy ruff UP035/TC003
- Use hasattr instead of isinstance(Protocol) for backend detection
  since runtime_checkable checks class attrs, not instance attrs,
  breaking MagicMock-based tests on Python 3.12+

Author: Patel230

src/hawk/memory_tools.py

@@ -13,7 +13,10 @@
 
 from __future__ import annotations
 
-from typing import Any, Protocol, Sequence, runtime_checkable
+from typing import TYPE_CHECKING, Any, Protocol, runtime_checkable
+
+if TYPE_CHECKING:
+    from collections.abc import Sequence
 
 from .tools import Tool
 
@@ -46,7 +49,9 @@ def __init__(self, client: Any, *, session_id: str | None = None) -> None:
         self._session_id = session_id
         self._local_memories: list[dict[str, str]] = []
         self._backend: MemoryBackend | None = (
-            client if isinstance(client, MemoryBackend) else None
+            client
+            if hasattr(client, "remember") and hasattr(client, "recall")
+            else None
         )
 
     def record_memory(