#499 port(ggml): in-place GDN state write + qwen dense decode recovery (lucebox-ggml #24, #27)

Ports two open ggml feature PRs from Luce-Org/lucebox-ggml into the in-tree vendored ggml (server/deps/llama.cpp/ggml/), on top of the vendorization from #486. Both were intentionally excluded from the initial snapshot (see VENDOR.md) and are brought in here.

Included

• lucebox-ggml #24 — perf(cuda): add in-place GDN state write (2576c152)
  Adds public API ggml_gated_delta_net_inplace, which writes the final recurrent state directly into src[5] via op_params[1]. Threads a state_out param through the CUDA GDN kernels. Default ggml_gated_delta_net behavior is unchanged.
• lucebox-ggml #27 — perf(cuda): recover qwen dense decode path (c3d44ed4)
  • Thread-local CUDA-graph props-check skip (ggml_cuda_set_skip_props_check) to bypass per-step graph re-validation on the stable AR decode path.
  • Compile-time WRITE_INTER template specialization of the GDN kernels — the pure-AR path compiles out the intermediate-state store entirely.
  • Ampere grouped-cols default flip (env DFLASH_GDN_FORCE_GROUPED_COLS / DFLASH_GDN_NO_GROUPED_COLS); grouped-cols is off by default on Ampere (sm_86 / 3090).

Notes

• The two upstream PRs overlap in gated_delta_net.cu; applied as the union (each kernel/launch signature carries both state_out and the WRITE_INTER template, with the runtime skip_intermediate param removed).
• Scope is ggml only — no consumer changes under server/src/. The new symbols are additive and unused by current server code.
• Commits keep original authorship.

Verification

• All target symbols present in the vendored tree.
• ggml.c, gated_delta_net.cu, and ggml-cuda.cu compile clean under CUDA 12.6 / sm_86 using the existing build flags.
• Diff limited to 4 files under server/deps/llama.cpp/ggml/; zero server/src/ drift.