Add mHC Sinkhorn CUDA kernel test

tests/unit/test_mhc_sinkhorn.py

@@ -0,0 +1,60 @@
+#!/usr/bin/env python3
+"""Test mHC Sinkhorn CUDA kernel — no fallback.
+
+Verifies:
+  1. Kernel compiles on sm_100a
+  2. Output matches PyTorch reference exactly (FP32, n=4, t_max=20)
+  3. Row sums = 1.0 ± 1e-5 (doubly stochastic)
+  4. Col sums = 1.0 ± 1e-5 (doubly stochastic)
+  5. Multiple batch sizes (T=1, 4, 8)
+"""
+
+import torch
+
+torch.manual_seed(42)
+device = 'cuda'
+
+from dsv4.kernels.cuda.loader import get_cuda_module
+mod = get_cuda_module("mhc_sinkhorn", ["mhc_sinkhorn.cu"])
+
+print("=" * 60)
+print("mHC Sinkhorn CUDA Kernel Test (NO FALLBACK)")
+print("=" * 60)
+
+n = 4; t_max = 20; eps = 1e-6
+
+def pytorch_sinkhorn(logits, t_max, eps):
+    M = torch.softmax(logits, dim=-1) + eps
+    M = M / (M.sum(dim=-2, keepdim=True) + eps)
+    for _ in range(t_max - 1):
+        M = M / (M.sum(dim=-1, keepdim=True) + eps)
+        M = M / (M.sum(dim=-2, keepdim=True) + eps)
+    return M
+
+for T in [1, 4, 8, 32]:
+    logits = torch.randn(T, n, n, device=device, dtype=torch.float32) * 3.0
+    
+    # CUDA kernel (NO fallback)
+    out_cuda = mod.mhc_sinkhorn(logits, t_max, eps)
+    
+    # PyTorch reference
+    out_ref = pytorch_sinkhorn(logits, t_max, eps)
+    
+    # Compare
+    cos = torch.nn.functional.cosine_similarity(out_cuda.flatten(), out_ref.flatten(), dim=0).item()
+    max_err = (out_cuda - out_ref).abs().max().item()
+    
+    # Check doubly stochastic
+    row_sums = out_cuda.sum(dim=-1)  # (T, n)
+    col_sums = out_cuda.sum(dim=-2)  # (T, n)
+    row_err = (row_sums - 1.0).abs().max().item()
+    col_err = (col_sums - 1.0).abs().max().item()
+    
+    print(f"  T={T:3d}: cos={cos:.8f} max_err={max_err:.2e} row_err={row_err:.2e} col_err={col_err:.2e}")
+    assert cos >= 0.9999, f"cos={cos:.8f} < 0.9999 at T={T}"
+    assert row_err < 1e-4, f"row_err={row_err:.2e} — NOT doubly stochastic!"
+    assert col_err < 1e-4, f"col_err={col_err:.2e} — NOT doubly stochastic!"
+
+print("\n" + "=" * 60)
+print("ALL mHC Sinkhorn TESTS PASSED")
+print("=" * 60)