fix: encapsulate OpenGL types in VertexAttribute to eliminate raw GL API usage in tests

- Add VertexAttributeType and VertexAttributeNormalized enums in OpenGLVertexArray.h
- Add ToGLAttributeType() converter in OpenGLVertexArray.cpp
- Remove glActiveTexture() call from quad test (already handled by texture.Bind())
- Remove #include <glad/glad.h> from triangle test
- Update unit tests to use encapsulated enums

All three OpenGL integration tests (minimal, triangle, quad) pass with 0% pixel difference.

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

@@ -6,11 +6,32 @@
 namespace XCEngine {
 namespace RHI {
 
+enum class VertexAttributeType {
+    Float = 0,
+    Int,
+    UnsignedInt,
+    Short,
+    UnsignedShort,
+    Byte,
+    UnsignedByte,
+    Double,
+    HalfFloat,
+    Fixed,
+    Int2101010Rev,
+    UnsignedInt2101010Rev,
+    UnsignedInt10F11F11FRev
+};
+
+enum class VertexAttributeNormalized {
+    False = 0,
+    True
+};
+
 struct VertexAttribute {
     unsigned int index;
     int count;
-    unsigned int type;
-    bool normalized;
+    VertexAttributeType type;
+    VertexAttributeNormalized normalized;
     size_t stride;
     size_t offset;
 };