chore: fix ruff linting and mypy issues in knowledge module

src/crewai/knowledge/source/string_knowledge_source.py

@@ -1,5 +1,3 @@
-from typing import List, Optional
-
 from pydantic import Field
 
 from crewai.knowledge.source.base_knowledge_source import BaseKnowledgeSource
@@ -9,7 +7,7 @@ class StringKnowledgeSource(BaseKnowledgeSource):
     """A knowledge source that stores and queries plain text content using embeddings."""
 
     content: str = Field(...)
-    collection_name: Optional[str] = Field(default=None)
+    collection_name: str | None = Field(default=None)
 
     def model_post_init(self, _):
         """Post-initialization method to validate content."""
@@ -26,7 +24,7 @@ class StringKnowledgeSource(BaseKnowledgeSource):
         self.chunks.extend(new_chunks)
         self._save_documents()
 
-    def _chunk_text(self, text: str) -> List[str]:
+    def _chunk_text(self, text: str) -> list[str]:
         """Utility method to split text into chunks."""
         return [
             text[i : i + self.chunk_size]