refactor(tests): Add strict type hints to third batch of test files

tests/test_gui_diagnostics.py

@@ -2,6 +2,7 @@ import pytest
 from unittest.mock import patch, MagicMock
 import importlib.util
 import sys
+from typing import Any
 import dearpygui.dearpygui as dpg
 
 # Load gui.py as a module for testing
@@ -29,14 +30,13 @@ def app_instance() -> None:
   yield app
  dpg.destroy_context()
 
-def test_diagnostics_panel_initialization(app_instance):
+def test_diagnostics_panel_initialization(app_instance: Any) -> None:
  assert "Diagnostics" in app_instance.window_info
  assert app_instance.window_info["Diagnostics"] == "win_diagnostics"
  assert "frame_time" in app_instance.perf_history
  assert len(app_instance.perf_history["frame_time"]) == 100
 
-def test_diagnostics_panel_updates(app_instance):
-# Mock dependencies
+def test_diagnostics_panel_updates(app_instance: Any) -> None:
  mock_metrics = {
   'last_frame_time_ms': 10.0,
   'fps': 100.0,