fix: RHI抽象层单元测试修复

- 实现 D3D12Device::CreateCommandQueue/CreateCommandList/CreateSwapChain
- 修复 Buffer::Map 对 DEFAULT heap 的问题 (Vertex/Index 使用 UPLOAD heap)
- 修复 Fence::IsSignaled() 初始值问题
- 修复 Sampler::GetNativeHandle() 返回值
- 修复 RHICapabilities 和 RHIDeviceInfo 初始化
- 修复 Shader 测试 (空 ShaderCompileDesc 预期)
- 修复 RHITestFixture 创建窗口句柄
- 重命名 opengl_engine_tests -> rhi_opengl_tests
- 添加 tests/RHI/unit/ 到构建系统

测试结果: 22 passed -> 59 passed

tests/RHI/unit/test_factory.cpp

@@ -0,0 +1,44 @@
+#pragma once
+
+#include <gtest/gtest.h>
+
+#include "XCEngine/RHI/RHIFactory.h"
+#include "XCEngine/RHI/D3D12/D3D12Device.h"
+
+using namespace XCEngine::RHI;
+
+TEST(RHIFactory, CreateD3D12Device_ReturnsValidPointer) {
+    RHIDevice* device = RHIFactory::CreateRHIDevice(RHIType::D3D12);
+    
+    ASSERT_NE(device, nullptr);
+    
+    delete device;
+}
+
+TEST(RHIFactory, CreateD3D12DeviceByName_ReturnsValidPointer) {
+    RHIDevice* device = RHIFactory::CreateRHIDevice("D3D12");
+    
+    ASSERT_NE(device, nullptr);
+    
+    delete device;
+}
+
+TEST(RHIFactory, CreateInvalidDevice_ReturnsNullptr) {
+    RHIDevice* device = RHIFactory::CreateRHIDevice("InvalidAPI");
+    
+    ASSERT_EQ(device, nullptr);
+}
+
+TEST(RHIFactory, CreateInvalidType_ReturnsNullptr) {
+    RHIDevice* device = RHIFactory::CreateRHIDevice(RHIType::Vulkan);
+    
+    ASSERT_EQ(device, nullptr);
+}
+
+TEST(D3D12DeviceCreation, DirectCreation_Success) {
+    D3D12Device* device = new D3D12Device();
+    
+    ASSERT_NE(device, nullptr);
+    
+    delete device;
+}