Add fetch option to retrieval_type type hint (#8)

Co-authored-by: Dan Jones <danjones@Dans-MacBook-Pro.local>

Author: danmichaeljones

src/engram/_models/memory.py

@@ -56,7 +56,7 @@ class ConversationContent:
 
 @dataclass(slots=True)
 class RetrievalConfig:
-    retrieval_type: Literal["vector", "bm25", "hybrid"]
+    retrieval_type: Literal["vector", "bm25", "hybrid", "fetch"]
     limit: int | None = None