third_party: bump llama.cpp to 710c7c23 — a separate MTP draft head loads and drafts on HRX (+53% decode) (closes #681) - #1252

Bumps third_party/llama.cpp c2c078b5 -> 710c7c23, the three commits of fork PR 1bit-MONSTER/llama.cpp#219 — a separate MTP draft head for qwen4exp now loads and drafts on HRX (engine#681):

1. src/llama-context.cpp: for EAGLE3/DFLASH/QWEN4EXP draft heads with no tok_embd/output and no ctx_other, warn instead of throw in the memory-fitting probe (the real draft context sets it in common_speculative_init; semantics unchanged);
2. src/llama-sampler.cpp: the backend support probe skips RESHAPE/VIEW/PERMUTE/TRANSPOSE metadata views, so HRX0 accepts the top-k sampler's candidate graph;
3. drop the unused fit-path hunk.

Measured (strixhalo, Qwen3.8-Flash-Next UD-IQ3_XXS, HRX0 -ngl 99 -c 32768 -np 1 -fa on --cache-reuse 256, house mtp-Qwen3.8-Flash-Next-shared-Q4_K_M.gguf, --spec-type draft-mtp --spec-draft-n-max 2, greedy 512 tokens, 1 rep)

The gain matches the issue's +55 % and the acceptance clears its 77 % bar; the draft adds ~3 GiB GTT.

Labelled deviations (not hidden)

• not clock-matched: the no-head arms' pp_dpm_sclk samples were lost with the expired ticket (head arms: 655-2857 / 1064-2803 MHz), so the rows are labelled rather than claimed as controlled;
• -ctv f16, not the issue's -ctv q4_0 (HRX rejects the q4_0 SET_ROWS node — see the new engine#1251);
• the medium row is 1,030 tokens, not the issue's 18,782: the long prompt dies in a pre-existing CPU-fallback SET_ROWS assert (ggml-cpu/ops.cpp:5136), reproduced without -md and on the unpatched fork tip -> filed as hrx: a >2k-token prompt dies in the CPU fallback of GGML_OP_SET_ROWS (out-of-range i1 assert), with or without -md #1251;
• 1 rep, not median-of-3.

Unproven: the long-context row, the q4_0 row, median-of-3. After this bump they can be re-run unchanged once #1251 (or a quiet window) allows.

Merge gate

Required context is build (the engine build does not compile HRX); the device table above is recorded on the fork PR and on engine#681. registry/architectures.json regenerated (sources: 710c7c23, 298/298) and tools/check_pins.py reports c2c078b58 -> 710c7c23c is ahead. Upstream pin move with a measured behaviour change; no RFC-relevant surface.