fix: resolve lint issues and test failures

- Remove unused imports from check_deps.py, flow_visualizer.py, and test files
- Add noqa comments for intentional imports in check_deps.py
- Fix PDF test to properly create temporary test file and handle missing dependencies
- Address all lint F401 errors identified in CI

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

tests/test_lite_installation.py

@@ -1,10 +1,6 @@
 """Test that crewAI lite installation works with minimal dependencies."""
 
 import pytest
-import subprocess
-import sys
-import tempfile
-import os
 from pathlib import Path
 from unittest.mock import patch, Mock