chore: fix ruff linting and mypy issues in knowledge module

src/crewai/knowledge/source/pdf_knowledge_source.py

@@ -1,5 +1,4 @@
 from pathlib import Path
-from typing import Dict, List
 
 from crewai.knowledge.source.base_file_knowledge_source import BaseFileKnowledgeSource
 
@@ -7,7 +6,7 @@ from crewai.knowledge.source.base_file_knowledge_source import BaseFileKnowledge
 class PDFKnowledgeSource(BaseFileKnowledgeSource):
     """A knowledge source that stores and queries PDF file content using embeddings."""
 
-    def load_content(self) -> Dict[Path, str]:
+    def load_content(self) -> dict[Path, str]:
         """Load and preprocess PDF file content."""
         pdfplumber = self._import_pdfplumber()
 
@@ -30,22 +29,22 @@ class PDFKnowledgeSource(BaseFileKnowledgeSource):
             import pdfplumber
 
             return pdfplumber
-        except ImportError:
+        except ImportError as e:
             raise ImportError(
                 "pdfplumber is not installed. Please install it with: pip install pdfplumber"
-            )
+            ) from e
 
     def add(self) -> None:
         """
         Add PDF file content to the knowledge source, chunk it, compute embeddings,
         and save the embeddings.
         """
-        for _, text in self.content.items():
+        for text in self.content.values():
             new_chunks = self._chunk_text(text)
             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]