ggml: Increase maximum graph size

The initial implementation of qwen3-vl:235b exceeded the maximum graph
size based on the number of tensors. Although this was later fixed
through the use of the mrope operation, we are close to the limit in
some cases. This updates to track the current llama.cpp usage of GGML.

ml/backend/ggml/ggml.go

@@ -378,7 +378,7 @@ func New(modelPath string, params ml.BackendParams) (ml.Backend, error) {
 		}
 	}
 
-	maxGraphNodes := max(8192, len(meta.Tensors().Items())*5)
+	maxGraphNodes := max(1024, len(meta.Tensors().Items())*8)
 
 	sched := C.ggml_backend_sched_new_ext(
 		(*C.ggml_backend_t)(unsafe.Pointer(&schedBackends[0])),