vulkan: add DeepSeek-V4 hyper-connection fused ops (DSV4_HC_COMB/PRE/POST) (#26578)

* vulkan: add DeepSeek-V4 hyper-connection fused ops (DSV4_HC_COMB/PRE/POST)

CUDA has these ops from the DeepSeek-V4 merge and Metal gained them in
PR 26459. Vulkan was the last major backend running the unfused primitive
chain. On DeepSeek-V4-Flash the unfused Sinkhorn comb chain alone takes
about 32% of decode op time on gfx1151 (Strix Halo), spread over roughly
16k dispatches per token.

dsv4_hc_comb runs the full 20-iteration Sinkhorn in registers. A token's
4x4 comb matrix lives in 16 consecutive subgroup lanes, with idst in bits
0-1 and isrc in bits 2-3 to match the CPU reference layout, so
subgroupShuffleXor by 1|2 reduces rows and by 4|8 reduces columns. One
dispatch replaces about 137 strictly ordered node executions per site.
The shuffle masks never cross a 16-lane boundary, so a subgroup of size
64 packs 4 independent tokens.

dsv4_hc_pre and dsv4_hc_post handle the elementwise stream collapse and
fan-out, with per-token coefficients staged in shared memory.

GGML_VK_DISABLE_DSV4_HC disables all three ops. The _COMB, _PRE and
_POST variants gate each op independently so a single kernel can be
bisected against the unfused graph.

Adds eval cases at the production n_iter=20 across batch sizes that
cross subgroup and workgroup boundaries.

* vulkan: dsv4 hc review fixes

Drop the per-op env-var disables and device flags, the stride divisibility
check (ggml guarantees it) and the workgroup-count fallback in supports_op.
Trim the comb shader comments to the lane layout.

---------

Co-authored-by: Kevin Hopper <no-reply@maestro.press>

tests/test-backend-ops.cpp

@@ -8807,6 +8807,11 @@ static std::vector<std::unique_ptr<test_case>> make_test_cases_eval() {
     test_cases.emplace_back(new test_dsv4_hc_comb(17, 4));
     test_cases.emplace_back(new test_dsv4_hc_comb(257, 8));
     test_cases.emplace_back(new test_dsv4_hc_comb(17, 20));
+    // production n_iter (DeepSeek-V4 uses 20) across batch sizes that cross
+    // subgroup and workgroup boundaries; 1 = single-token decode
+    for (int64_t n_tokens : {1, 256, 336, 512, 513, 1024, 2048}) {
+        test_cases.emplace_back(new test_dsv4_hc_comb(n_tokens, 20));
+    }
 
     test_cases.emplace_back(new test_dsv4_hc_pre(1, 1));
     test_cases.emplace_back(new test_dsv4_hc_pre(31, 17));