Fix crashes and SPIRV compatibility on Raytracing.

[RowDaBoat]

Summary

Ray tracing pipeline and bind group creation could crash the Vulkan driver: a
dangling pointer into a caller-owned chain struct could get read after the
caller freed it, and raw-SPIR-V-sourced ray tracing shaders got a
VK_NULL_HANDLE shader module in the SBT.

Fixes

• Deep-copy the WGPUBindGroupLayoutEntryRayTracing chain in wgpuDeviceCreateBindGroupLayout to avoid a dangling pointer once the caller's chain struct is freed.
• Free the deep-copied nextInChain entries in wgpuBindGroupLayoutRelease.
• Use vulkanModuleMultiEP when building the ray tracing SBT's shader stages.

Verification

• I verified the fixes work using wgvk's raytracing.c example.
• I tested the SPIR-V path on my own engine, can add an example later if necessary.

[manuel5975p]

lgtm, the failing tests are Zig only