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/CMakeLists.txt

@@ -5,41 +5,5 @@ project(RHIEngineTests)
 set(CMAKE_CXX_STANDARD 17)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 
-get_filename_component(PROJECT_ROOT_DIR ${CMAKE_CURRENT_SOURCE_DIR}/../../.. ABSOLUTE)
-
-find_package(OpenGL REQUIRED)
-
-include_directories(${CMAKE_SOURCE_DIR}/tests/OpenGL/package/include/)
-include_directories(${PROJECT_ROOT_DIR}/engine/include)
-include_directories(${PROJECT_ROOT_DIR}/engine/src)
-
-link_directories(${CMAKE_SOURCE_DIR}/tests/OpenGL/package/lib/)
-
-find_package(GTest REQUIRED)
-
-set(TEST_SOURCES
-    test_factory.cpp
-)
-
-add_executable(rhi_engine_tests ${TEST_SOURCES})
-
-target_link_libraries(rhi_engine_tests PRIVATE
-    opengl32
-    glfw3
-    d3d12
-    dxgi
-    d3dcompiler
-    XCEngine
-    GTest::gtest
-    GTest::gtest_main
-)
-
-target_include_directories(rhi_engine_tests PRIVATE
-    ${PROJECT_ROOT_DIR}/engine/include
-    ${PROJECT_ROOT_DIR}/engine/src
-)
-
-enable_testing()
-add_test(NAME RHIEngineTests COMMAND rhi_engine_tests)
-
-add_subdirectory(unit)
+add_subdirectory(D3D12)
+add_subdirectory(OpenGL)