fix(vulkan-rt): merge TLAS push constant into existing block (#18)

The NVIDIA descriptor-heap AS-read workaround (#15) rewrote heap
acceleration-structure reads into a load of the TLAS device address from
a push-constant block. It always *synthesized a new* push-constant block,
so any ray-tracing shader that already declared one ended up with two —
which SPIR-V forbids ("at most one push constant block statically used per
entry point"), and vkCreateShaderModule's spirv-val check rejected:

    Entry point id '4' uses more than one PushConstant interface.

WorkaroundNvidiaAS::Patch now detects an existing PushConstant variable and,
when present, appends a single ulong member (the TLAS address) to that
block instead of adding a second one, reading the address through the
shader's own push-constant variable. The append offset is the end of the
user's block, computed from the members' explicit Offset/ArrayStride/
MatrixStride decorations (correct under both scalar and std140 layout) and
rounded up to 8. Shaders with no push constant of their own keep getting a
freshly synthesized single-member block at offset 0, exactly as before.

That offset is published via Device::workaroundTlasPushOffset and RTPass
feeds it to vkCmdPushDataEXT so the address lands where the rewritten load
reads it (0 for the synthesized case, preserving prior behaviour).

Verified on the affected driver (NVIDIA 610.43.02, RTX 4090): VulkanTriangle
ray-traces correctly and validation-clean both with and without a
user-declared raygen push constant.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

interfaces/Crafter.Graphics-RTPass.cppm

@@ -46,7 +46,10 @@ export namespace Crafter {
                 VkDeviceAddress tlasAddr = RenderingElement3D::tlases[frameIdx].address;
                 VkPushDataInfoEXT pushInfo {
                     .sType  = VK_STRUCTURE_TYPE_PUSH_DATA_INFO_EXT,
-                    .offset = 0,
+                    // Where the rewritten raygen reads the TLAS address: 0 when
+                    // VulkanShader synthesized a fresh block, or the offset of
+                    // the member it appended to the shader's existing block.
+                    .offset = Device::workaroundTlasPushOffset,
                     .data   = { .address = &tlasAddr, .size = sizeof(tlasAddr) },
                 };
                 Device::vkCmdPushDataEXT(cmd, &pushInfo);