refactorize networks, now can be used cross platform (#3141)

Co-authored-by: Han Wang <[email protected]>

Author: wanghan-iapcm

deepmd_utils/model_format/__init__.py

@@ -14,6 +14,9 @@
     NativeNet,
     NetworkCollection,
     load_dp_model,
+    make_embedding_network,
+    make_fitting_network,
+    make_multilayer_network,
     save_dp_model,
     traverse_model_dict,
 )
@@ -32,6 +35,9 @@
 __all__ = [
     "DescrptSeA",
     "EnvMat",
+    "make_multilayer_network",
+    "make_embedding_network",
+    "make_fitting_network",
     "EmbeddingNet",
     "FittingNet",
     "NativeLayer",