feat: add configurable search parameters for RAG, knowledge, and memory (#3531)

- Add limit and score_threshold to BaseRagConfig, propagate to clients  
- Update default search params in RAG storage, knowledge, and memory (limit=5, threshold=0.6)  
- Fix linting (ruff, mypy, PERF203) and refactor save logic  
- Update tests for new defaults and ChromaDB behavior

src/crewai/memory/storage/mem0_storage.py

@@ -151,7 +151,7 @@ class Mem0Storage(Storage):
         self.memory.add(conversations, **params)
 
     def search(
-        self, query: str, limit: int = 3, score_threshold: float = 0.35
+        self, query: str, limit: int = 5, score_threshold: float = 0.6
     ) -> list[Any]:
         params = {
             "query": query,