feat: support for cross-device row split (#1735)

include/stable-diffusion.h

@@ -227,6 +227,7 @@ typedef struct {
     bool eager_load;  // Load all params into the params backend at model-load time instead of lazily on first use
     const char* backend;
     const char* params_backend;
+    const char* split_mode;  // weight distribution for multi-device modules: layer (default) or row, or per-module assignments e.g. "diffusion=row"
     const char* rpc_servers;
 } sd_ctx_params_t;