refactor: improve test infrastructure and fix OpenGL GLAD initialization

- Rename D3D12Enum.h to D3D12Enums.h for naming consistency
- Fix OpenGL unit test GLAD initialization by using gladLoadGL()
  instead of gladLoadGLLoader(wglGetProcAddress) for fallback support
- Migrate remaining tests to use gtest_discover_tests for granular
  test discovery (math, core, containers, memory, threading, debug,
  components, scene, resources, input, opengl)
- Remove obsolete TEST_RESOURCES_DIR and copy_directory commands
  from OpenGL unit test CMakeLists (minimal/Res doesn't exist)
- Update TEST_SPEC.md with performance metrics and per-module
  build/test commands for faster development workflow
- Update CMake path references to use lowercase paths

tests/debug/CMakeLists.txt

@@ -1,14 +1,16 @@
-add_executable(xcengine_debug_tests
+find_package(GTest REQUIRED)
+
+add_executable(debug_tests
     test_logger.cpp
     test_profiler.cpp
 )
 
-target_link_libraries(xcengine_debug_tests
+target_link_libraries(debug_tests
     PRIVATE
     XCEngine
-    gtest
-    gtest_main
+    GTest::gtest
+    GTest::gtest_main
 )
 
 include(GoogleTest)
-gtest_discover_tests(xcengine_debug_tests)
+gtest_discover_tests(debug_tests)