fix: resolve lint and type issues in Google Batch Mode implementation

- Fix unused imports in test_batch_mode.py
- Update Google GenAI API calls to use correct client.batches methods
- Add proper type annotations and error handling
- Ensure compatibility with google-generativeai SDK

Co-Authored-By: João <joao@crewai.com>

tests/test_batch_mode.py

@@ -1,7 +1,6 @@
 import pytest
-import time
-from unittest.mock import Mock, patch, MagicMock
-from crewai.llm import LLM, BatchJobStartedEvent, BatchJobCompletedEvent, BatchJobFailedEvent
+from unittest.mock import Mock, patch
+from crewai.llm import LLM
 
 
 class TestBatchMode: