RHI: Refactor Fence module to pure timeline semantics

- Remove IsSignaled() from RHIFence interface (semantic inconsistency)
- Remove Reset() from OpenGL implementation (no D3D12 counterpart)
- OpenGL Fence now uses single GLsync + CPU counters for timeline simulation
- OpenGL Fence Initialize() now accepts uint64_t initialValue (was bool)
- Add comprehensive timeline semantics tests for all backends:
  - Signal increment/decrement scenarios
  - Multiple signals
  - Wait smaller than completed value
  - GetCompletedValue stages verification
- Update documentation to reflect actual implementation

engine/include/XCEngine/RHI/D3D12/D3D12Fence.h

@@ -22,7 +22,6 @@ public:
     void Signal(uint64_t value) override;
     void Wait(uint64_t value) override;
     uint64_t GetCompletedValue() const override;
-    bool IsSignaled() const override { return m_fence->GetCompletedValue() >= m_signalValue; }
     void* GetEventHandle() { return m_eventHandle; }
 
     void* GetNativeHandle() override { return m_fence.Get(); }
@@ -31,7 +30,6 @@ public:
 private:
     ComPtr<ID3D12Fence> m_fence;
     void* m_eventHandle;
-    uint64_t m_signalValue = UINT64_MAX;
 };
 
 } // namespace RHI

engine/include/XCEngine/RHI/OpenGL/OpenGLFence.h

@@ -1,44 +1,34 @@
 #pragma once
 
 #include <cstdint>
+#include <atomic>
 
 #include "../RHIFence.h"
 
 namespace XCEngine {
 namespace RHI {
 
-enum class FenceStatus {
-    Signaled,
-    Unsignaled,
-    Error
-};
-
 class OpenGLFence : public RHIFence {
 public:
     OpenGLFence();
     ~OpenGLFence() override;
 
-    bool Initialize(bool signaled = false);
+    bool Initialize(uint64_t initialValue = 0);
     void Shutdown() override;
 
     void Signal() override;
     void Signal(uint64_t value) override;
     void Wait(uint64_t value) override;
-    void Reset();
 
-    bool IsSignaled() const override;
-    FenceStatus GetStatus() const;
     uint64_t GetCompletedValue() const override;
-    uint64_t GetCurrentValue() const { return m_fenceValue; }
 
     void* GetNativeHandle() override;
 
 private:
     void* m_sync;
-    uint64_t m_fenceValue;
-    uint64_t m_completedValue;
-    bool m_signaled;
+    std::atomic<uint64_t> m_signaledValue;
+    std::atomic<uint64_t> m_completedValue;
 };
 
 } // namespace RHI
-} // namespace XCEngine
+} // namespace XCEngine

engine/include/XCEngine/RHI/RHIFence.h

@@ -15,7 +15,6 @@ public:
     virtual void Signal(uint64_t value) = 0;
     virtual void Wait(uint64_t value) = 0;
     virtual uint64_t GetCompletedValue() const = 0;
-    virtual bool IsSignaled() const = 0;
 
     virtual void* GetNativeHandle() = 0;
 };