Added Embree CPU backend, hybrid context, and hybrid ray tracing API

[krisu011]

Added:

• Phase 1: ContextBase, refactor Context → GpuContext, context routing in hiprtCreateContext
• Phase 2: CpuContext (Embree), hiprt_cpu.h with traceBatch (closest + any-hit), CPU tests
• Phase 3: HybridContext — GPU handles outward, Embree mirrors in side-tables + CpuDataRegistry
• Phase 4: hiprt_hybrid.h / hiprtTraceHybridClosest + hiprtTraceHybridAnyHit (scene + geometry), GPU/CPU batch split (gpuFraction), internal batch-kernel compile and cache

Tests:
20 CPU+Hybrid tests: CpuTest., HybridTest.

To run tests:
.\dist\bin\Release\unittest64.exe --gtest_filter=CpuTest.:HybridTest.