refactor: Improve agentops integration with better types and tests

- Add specific error handling for agentops initialization
- Add type hints for better code readability
- Improve API key validation
- Reorganize tests using pytest fixtures and classes
- Add documentation for set_private_attrs method

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

src/crewai/crew.py

@@ -53,8 +53,6 @@ from crewai.utilities.planning_handler import CrewPlanner
 from crewai.utilities.task_output_storage_handler import TaskOutputStorageHandler
 from crewai.utilities.training_handler import CrewTrainingHandler
 
-from typing import Optional
-
 try:
     import agentops  # type: ignore
     from agentops.exceptions import AgentOpsError, AuthenticationError  # type: ignore