[Metal] Add ray tracing pipeline, SBT, and DispatchRays bring-up

[MarijnS95]

Depends on #1275

Summary

Last backend in the PSO RT bring-up stack. DXR-style ray tracing reaches Metal through metal_irconverter: each RT entry point is lowered from DXIL to a Metal IR function, raygen is emitted as a kernel (IRRayGenerationCompilationKernel) so it can be dispatched directly, and miss / closest-hit / any-hit / intersection / callable functions are emitted as visible functions and pulled into a MTLVisibleFunctionTable.

Fills in the three virtuals the foundation PR left stubbed on Metal:

• MTLDevice::createPipelineRT compiles every Shaders[] entry against a single IRRayTracingPipelineConfiguration (max attribute / recursion budget from the YAML RTConfig), builds one MTL::Library per entry, hands the raygen function to the compute pipeline as the kernel, and registers the rest as LinkedFunctions. The freshly-built pipeline then mints a MTLVisibleFunctionTable and resolves each callable function's handle into a slot index that the SBT builder reuses. setMaxCallStackDepth(MaxTraceRecursionDepth) is set so nested TraceRay actually unwinds (default of 1 silently drops the second trace).
• MTLDevice::createShaderBindingTable lays the four SBT regions out via the shared computeSBTLayout helper sized for IRShaderIdentifier records, looks up each region entry's ShaderName in the pipeline's name → IRShaderIdentifier map, and memcpys the records into a shared-storage MTL::Buffer the runtime dereferences at dispatch.
• MTLComputeEncoder::dispatchRays binds the raygen pipeline and runs dispatchThreads(Width, Height, Depth) on the encoder. The caller (createRayTracingCommands in MTLDevice) builds the per-dispatch IRDispatchRaysArgument struct (SBT region addresses + sizes, GRS / ResDescHeap GPU pointers, visible / intersection function table resourceIDs), parks it in a shared MTL::Buffer kept alive on the command buffer's KeepAlive list, and binds it at kIRRayDispatchArgumentsBindPoint so callees reached via TraceRay() inherit the same dispatch state through that pointer.

Plumbs the existing executeProgram RT branch on Metal the same way the VK / DX backends already do (validate Shaders / SBT / RTConfig, build RayTracingPipelineCreateDesc from the YAML pipeline, create PSO, build SBT, record commands), and adds the raytracing-pipeline lit feature on Metal so test/Feature/RT/raygen-roundtrip.test drops Metal from its XFAIL list and passes natively on Apple Silicon.

This bring-up only handles Triangle hit groups whose only member is a ClosestHit shader — any-hit / intersection / procedural / local root signatures land in follow-ups; createPipelineRT returns a clear unsupported error for those shapes instead of silently producing wrong output.

Test plan

Local on an NVIDIA RTX 3060:

• Linux Vulkan (native offloader)
• Linux D3D12 (Wine + vkd3d-proton + cross-compiled offloader.exe)
• Windows Vulkan (native offloader.exe)
• Windows D3D12 (native offloader.exe)

CI (RT-capable runners):

• windows-nvidia D3D12 (RaytracingTier 1.2)
• windows-intel VK (VK_KHR_ray_tracing_pipeline)
• macOS Metal (supportsRaytracing)