fix(rebase): adapt to dev's split tensor_upload/_g API + fault-injection hook

Dev split coli_cuda_tensor_upload into two symbols: the plain 7-arg
tensor_upload (no gs) for fmt!=4, and tensor_upload_g (8-arg, with gs)
for fmt=4 grouped. The DLL-side _g sets a g_upload_gs global the plain
upload reads internally. Adapted all call sites:

- colibri.c: qt_cuda_upload already dispatches (_g for fmt=4, plain
  otherwise) — kept dev's version. layer_cuda_shard_kvb was calling the
  plain upload with gs; switched to tensor_upload_g.
- backend_loader.c: the C-API wrapper matches dev's 7-arg signature;
  tensor_upload_g dispatched separately.
- backend_cuda.cu: cache-hit check uses g_upload_gs (not a gs param);
  coli_cuda_matmul dispatches _g when gs>0; the grouped-expert host
  fallback quant_matmul calls pass gs=0,ng=1 (host tier is per-row).
- Kept dev's fault-injection hook, scale_count field, and fmt=4 support
  in the grouped-expert path (all_q4/any_g4 tracking).
- tests: kept dev's comprehensive tensor_upload test (cached reuse,
  temp-buffer survival, upload-failure accounting, fault injection).

Build-verified: colibri.exe + coli_cuda.dll both compile clean.

c/backend_cuda.h

@@ -41,7 +41,7 @@ COLI_CUDA_DLLEXPORT int coli_cuda_tensor_upload_g(ColiCudaTensor **tensor,
         int fmt, int I, int O, int device, int gs);
 COLI_CUDA_DLLEXPORT int coli_cuda_tensor_upload(ColiCudaTensor **tensor,
                             const void *weights, const float *scales,
-                            int fmt, int I, int O, int device, int gs);
+                            int fmt, int I, int O, int device);
 
 /*
  * y[S,O] = x[S,I] @ W[O,I]^T.