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>

src/crewai/flow/flow_visualizer.py

@@ -1,7 +1,6 @@
 # flow_visualizer.py
 
 import os
-from pathlib import Path
 
 try:
     from pyvis.network import Network
@@ -13,7 +12,7 @@ except ImportError:
 from crewai.flow.config import COLORS, NODE_STYLES
 from crewai.flow.html_template_handler import HTMLTemplateHandler
 from crewai.flow.legend_generator import generate_legend_items_html, get_legend_items
-from crewai.flow.path_utils import safe_path_join, validate_path_exists
+from crewai.flow.path_utils import safe_path_join
 from crewai.flow.utils import calculate_node_levels
 from crewai.flow.visualization_utils import (
     add_edges,