Implement Intel Embree CPU Fallback and Zero-Copy Hybrid Mode for APUs

[Tsokko]

This PR introduces a hardware-agnostic C++ architecture to HIPRT, adding software ray tracing fallback via Intel Embree and a Zero-Copy Hybrid Mode for AMD APUs.

Added:

Phase 1: ContextBase, refactor monolithic Context → GpuContext, context routing in hiprtCreateContext
Phase 2: CpuContext (Embree), hiprt_cpu.h with SIMD AVX vectorization for rtcIntersect8, CPU-side BVH building
Phase 3: HybridContext — Zero-Copy memory sharing between CPU/GPU using oroMallocManaged & HSA_XNACK=1
Phase 4: hiprt_hybrid.h / Dual Dispatch load balancing (gpuFraction) to saturate both processors asynchronously
Tests: 38 passing Unit Tests on AMD APU hardware without RT cores.

To run tests:

.\dist\bin\Release\unittest64.exe --gtest_filter="hiprtTest*:Obj*"