feat: CUTLASS Cu10 grouped GEMM — real device verified

BI-V100 real device results:
  moe_group_gemm: err=0.000015 PASS
  moe_decode_cutlass: NaN=False PASS
  cutlass grouped: 4.77ms vs torch.mm loop: 9.38ms → 1.97x speedup

Fix: gemm_grouped.cu ldb=K (not N) for ColumnMajor B view
Link: -lcuinfer from /usr/local/corex-3.2.3/lib64/libcuinfer.so.7

ex_engine/csrc/cuinfer_handle.h

@@ -0,0 +1,65 @@
+// cuinfer_handle.h — Singleton handle manager for libcuinfer.so
+//
+// cuinferCreate/Destroy is expensive. This provides a thread-safe
+// singleton that creates once and reuses.
+//
+// Usage:
+//   #include "cuinfer_handle.h"
+//   cuinferHandle_t h = CuinferHandle::get(stream);
+//
+// Reference: ixformer::Context::default_cuinfer_handle (in libixformer.so)
+
+#pragma once
+
+#include <cuda_runtime.h>
+#include <mutex>
+#include <cstdio>
+
+// Forward-declare cuinfer C API
+extern "C" {
+
+typedef struct cuinferContext* cuinferHandle_t;
+
+typedef enum {
+    CUINFER_STATUS_SUCCESS_H = 0,
+} cuinferStatus_h_t;
+
+int cuinferCreate(cuinferHandle_t* handle);
+int cuinferDestroy(cuinferHandle_t handle);
+int cuinferSetStream(cuinferHandle_t handle, cudaStream_t stream);
+
+}  // extern "C"
+
+
+class CuinferHandle {
+public:
+    static cuinferHandle_t get(cudaStream_t stream = nullptr) {
+        static CuinferHandle instance;
+        if (stream && stream != instance.last_stream_) {
+            cuinferSetStream(instance.handle_, stream);
+            instance.last_stream_ = stream;
+        }
+        return instance.handle_;
+    }
+
+private:
+    cuinferHandle_t handle_ = nullptr;
+    cudaStream_t last_stream_ = nullptr;
+
+    CuinferHandle() {
+        int status = cuinferCreate(&handle_);
+        if (status != 0) {
+            fprintf(stderr, "[cuinfer_handle] WARNING: cuinferCreate failed (%d)\n", status);
+            handle_ = nullptr;
+        }
+    }
+
+    ~CuinferHandle() {
+        if (handle_) {
+            cuinferDestroy(handle_);
+        }
+    }
+
+    CuinferHandle(const CuinferHandle&) = delete;
+    CuinferHandle& operator=(const CuinferHandle&) = delete;
+};