RHI: Replace IsFinalized/Finalize with IsValid/EnsureValid

Unified PSO validation semantics across D3D12 and OpenGL backends:
- IsValid() returns whether PSO is ready to use
- EnsureValid() ensures PSO is valid (compiles if needed)

Behavior by backend:
- D3D12: IsValid=false after creation, true after EnsureValid() with shaders
- OpenGL: IsValid always=true (immediate model)

Also added test_pipeline_state.cpp with 10 tests for RHIPipelineState.

tests/RHI/unit/test_pipeline_state.cpp

@@ -0,0 +1,172 @@
+#include "fixtures/RHITestFixture.h"
+#include "XCEngine/RHI/RHIPipelineState.h"
+#include <cstring>
+
+using namespace XCEngine::RHI;
+
+TEST_P(RHITestFixture, PipelineState_Create_DefaultDesc) {
+    GraphicsPipelineDesc desc = {};
+    RHIPipelineState* pso = GetDevice()->CreatePipelineState(desc);
+    if (pso != nullptr) {
+        if (GetBackendType() == RHIType::D3D12) {
+            EXPECT_FALSE(pso->IsValid());
+        } else {
+            EXPECT_TRUE(pso->IsValid());
+        }
+        pso->Shutdown();
+        delete pso;
+    }
+}
+
+TEST_P(RHITestFixture, PipelineState_SetGet_RasterizerState) {
+    GraphicsPipelineDesc desc = {};
+    RHIPipelineState* pso = GetDevice()->CreatePipelineState(desc);
+    ASSERT_NE(pso, nullptr);
+    
+    RasterizerDesc rasterizer = {};
+    rasterizer.fillMode = 2;
+    rasterizer.cullMode = 2;
+    rasterizer.depthClipEnable = true;
+    pso->SetRasterizerState(rasterizer);
+    
+    const RasterizerDesc& retrieved = pso->GetRasterizerState();
+    EXPECT_EQ(retrieved.cullMode, 2u);
+    EXPECT_EQ(retrieved.fillMode, 2u);
+    
+    pso->Shutdown();
+    delete pso;
+}
+
+TEST_P(RHITestFixture, PipelineState_SetGet_BlendState) {
+    GraphicsPipelineDesc desc = {};
+    RHIPipelineState* pso = GetDevice()->CreatePipelineState(desc);
+    ASSERT_NE(pso, nullptr);
+    
+    BlendDesc blend = {};
+    blend.blendEnable = true;
+    blend.srcBlend = 1;
+    blend.dstBlend = 0;
+    pso->SetBlendState(blend);
+    
+    const BlendDesc& retrieved = pso->GetBlendState();
+    EXPECT_TRUE(retrieved.blendEnable);
+    EXPECT_EQ(retrieved.srcBlend, 1u);
+    
+    pso->Shutdown();
+    delete pso;
+}
+
+TEST_P(RHITestFixture, PipelineState_SetGet_DepthStencilState) {
+    GraphicsPipelineDesc desc = {};
+    RHIPipelineState* pso = GetDevice()->CreatePipelineState(desc);
+    ASSERT_NE(pso, nullptr);
+    
+    DepthStencilStateDesc ds = {};
+    ds.depthTestEnable = true;
+    ds.depthWriteEnable = true;
+    ds.depthFunc = 3;
+    pso->SetDepthStencilState(ds);
+    
+    const DepthStencilStateDesc& retrieved = pso->GetDepthStencilState();
+    EXPECT_TRUE(retrieved.depthTestEnable);
+    EXPECT_TRUE(retrieved.depthWriteEnable);
+    EXPECT_EQ(retrieved.depthFunc, 3u);
+    
+    pso->Shutdown();
+    delete pso;
+}
+
+TEST_P(RHITestFixture, PipelineState_SetGet_InputLayout) {
+    GraphicsPipelineDesc desc = {};
+    RHIPipelineState* pso = GetDevice()->CreatePipelineState(desc);
+    ASSERT_NE(pso, nullptr);
+    
+    InputElementDesc element = {};
+    element.semanticName = "POSITION";
+    element.semanticIndex = 0;
+    element.format = static_cast<uint32_t>(Format::R32G32B32A32_Float);
+    element.inputSlot = 0;
+    element.alignedByteOffset = 0;
+    
+    InputLayoutDesc layoutDesc = {};
+    layoutDesc.elements.push_back(element);
+    pso->SetInputLayout(layoutDesc);
+    
+    const InputLayoutDesc& retrieved = pso->GetInputLayout();
+    ASSERT_EQ(retrieved.elements.size(), 1u);
+    EXPECT_EQ(retrieved.elements[0].semanticName, "POSITION");
+    
+    pso->Shutdown();
+    delete pso;
+}
+
+TEST_P(RHITestFixture, PipelineState_SetTopology) {
+    GraphicsPipelineDesc desc = {};
+    RHIPipelineState* pso = GetDevice()->CreatePipelineState(desc);
+    ASSERT_NE(pso, nullptr);
+    
+    pso->SetTopology(3);
+    
+    pso->Shutdown();
+    delete pso;
+}
+
+TEST_P(RHITestFixture, PipelineState_SetRenderTargetFormats) {
+    GraphicsPipelineDesc desc = {};
+    RHIPipelineState* pso = GetDevice()->CreatePipelineState(desc);
+    ASSERT_NE(pso, nullptr);
+    
+    uint32_t formats[] = { static_cast<uint32_t>(Format::R8G8B8A8_UNorm) };
+    pso->SetRenderTargetFormats(1, formats, static_cast<uint32_t>(Format::D24_UNorm_S8_UInt));
+    
+    pso->Shutdown();
+    delete pso;
+}
+
+TEST_P(RHITestFixture, PipelineState_EnsureValid_IsValid) {
+    GraphicsPipelineDesc desc = {};
+    desc.renderTargetFormats[0] = static_cast<uint32_t>(Format::R8G8B8A8_UNorm);
+    desc.depthStencilFormat = static_cast<uint32_t>(Format::D24_UNorm_S8_UInt);
+    
+    RHIPipelineState* pso = GetDevice()->CreatePipelineState(desc);
+    ASSERT_NE(pso, nullptr);
+    
+    if (GetBackendType() == RHIType::D3D12) {
+        EXPECT_FALSE(pso->IsValid());
+        pso->EnsureValid();
+        EXPECT_FALSE(pso->IsValid());
+    } else {
+        EXPECT_TRUE(pso->IsValid());
+        pso->EnsureValid();
+        EXPECT_TRUE(pso->IsValid());
+    }
+    
+    pso->Shutdown();
+    delete pso;
+}
+
+TEST_P(RHITestFixture, PipelineState_Shutdown_Invalidates) {
+    GraphicsPipelineDesc desc = {};
+    desc.renderTargetFormats[0] = static_cast<uint32_t>(Format::R8G8B8A8_UNorm);
+    desc.depthStencilFormat = static_cast<uint32_t>(Format::D24_UNorm_S8_UInt);
+    
+    RHIPipelineState* pso = GetDevice()->CreatePipelineState(desc);
+    ASSERT_NE(pso, nullptr);
+    
+    pso->EnsureValid();
+    pso->Shutdown();
+    pso->Shutdown();
+    delete pso;
+}
+
+TEST_P(RHITestFixture, PipelineState_GetType) {
+    GraphicsPipelineDesc desc = {};
+    RHIPipelineState* pso = GetDevice()->CreatePipelineState(desc);
+    ASSERT_NE(pso, nullptr);
+    
+    PipelineType type = pso->GetType();
+    EXPECT_EQ(type, PipelineType::Graphics);
+    
+    pso->Shutdown();
+    delete pso;
+}