refactor(tests): reorganize tests directory to match engine structure

- Created tests/Core/Asset/ with tests for IResource, ResourceTypes, ResourceHandle, ResourceCache, ResourceDependencyGraph, ResourceGUID
- Created tests/Core/IO/ with tests for IResourceLoader, ResourcePath, ResourceFileSystem, FileArchive, ResourcePackage
- Reorganized tests/Resources/ into subdirectories: Texture/, Mesh/, Material/, Shader/, AudioClip/
- Added CMakeLists.txt for each new test subdirectory
- Fixed Material.h missing ResourceManager.h include (lost during engine refactor)
- tests/Core/CMakeLists.txt updated to include Asset/ and IO/ subdirectories

tests/Resources/AudioClip/test_audio_clip.cpp

@@ -0,0 +1,20 @@
+#include <gtest/gtest.h>
+#include <XCEngine/Resources/AudioClip/AudioClip.h>
+#include <XCEngine/Core/Asset/ResourceTypes.h>
+#include <XCEngine/Core/Asset/ResourceManager.h>
+
+using namespace XCEngine::Resources;
+
+namespace {
+
+TEST(AudioClip, GetType) {
+    AudioClip audio;
+    EXPECT_EQ(audio.GetType(), ResourceType::AudioClip);
+}
+
+TEST(AudioClip, GetMemorySize) {
+    AudioClip audio;
+    EXPECT_EQ(audio.GetMemorySize(), 0u);
+}
+
+} // namespace