feat: add MTP speculative decoding support

[jhen0409]

Summary

• Add native MTP speculative decoding support and TypeScript API/result fields.
• Add an independent example app screen for MTP with the ggml-org/Qwen3.6-35B-A3B-MTP-GGUF model. (M3 Max MacBook Pro)
• Add a Metal shader compatibility patch for the Q8_0 MoE kernel_mul_mv_id pipeline and keep it in bootstrap patches.
• Document MTP usage and constraints in the README.

Validation

• npm run typecheck
• npm run lint
• npm test -- --runInBand
• git diff --check
• ./tests/build_and_test.sh
• ./tests/run_tests.sh
• xcrun -sdk iphoneos metal -c cpp/ggml-metal/ggml-metal.metal
• Local MTLDevice pipeline creation for kernel_mul_mv_id_q8_0_f32 with nsg=4