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/RHI/OpenGL/integration/sphere/CMakeLists.txt

@@ -0,0 +1,57 @@
+cmake_minimum_required(VERSION 3.15)
+
+set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR})
+
+project(OpenGL_Sphere)
+
+set(ENGINE_ROOT_DIR ${CMAKE_SOURCE_DIR}/engine)
+set(PACKAGE_DIR ${CMAKE_SOURCE_DIR}/tests/opengl/package)
+
+add_executable(OpenGL_Sphere
+    WIN32
+    main.cpp
+    ${PACKAGE_DIR}/src/glad.c
+)
+
+target_include_directories(OpenGL_Sphere PRIVATE
+    ${CMAKE_CURRENT_SOURCE_DIR}
+    ${ENGINE_ROOT_DIR}/include
+    ${PACKAGE_DIR}/include
+)
+
+target_link_libraries(OpenGL_Sphere PRIVATE
+    opengl32
+    XCEngine
+)
+
+target_compile_definitions(OpenGL_Sphere PRIVATE
+    UNICODE
+    _UNICODE
+)
+
+add_custom_command(TARGET OpenGL_Sphere POST_BUILD
+    COMMAND ${CMAKE_COMMAND} -E copy_directory
+        ${CMAKE_CURRENT_SOURCE_DIR}/Res
+        $<TARGET_FILE_DIR:OpenGL_Sphere>/Res
+)
+
+add_custom_command(TARGET OpenGL_Sphere POST_BUILD
+    COMMAND ${CMAKE_COMMAND} -E copy_if_different
+        ${CMAKE_SOURCE_DIR}/tests/rhi/opengl/integration/run_integration_test.py
+        $<TARGET_FILE_DIR:OpenGL_Sphere>/
+    COMMAND ${CMAKE_COMMAND} -E copy_if_different
+        ${CMAKE_SOURCE_DIR}/tests/rhi/opengl/integration/compare_ppm.py
+        $<TARGET_FILE_DIR:OpenGL_Sphere>/
+    COMMAND ${CMAKE_COMMAND} -E copy_if_different
+        ${CMAKE_CURRENT_SOURCE_DIR}/GT.ppm
+        $<TARGET_FILE_DIR:OpenGL_Sphere>/
+)
+
+add_test(NAME OpenGL_Sphere_Integration
+    COMMAND ${Python3_EXECUTABLE} $<TARGET_FILE_DIR:OpenGL_Sphere>/run_integration_test.py
+        $<TARGET_FILE:OpenGL_Sphere>
+        sphere.ppm
+        ${CMAKE_CURRENT_SOURCE_DIR}/GT.ppm
+        5
+    WORKING_DIRECTORY $<TARGET_FILE_DIR:OpenGL_Sphere>
+)