optimize: move slicer2, rmvpe, my_utils to lib

vc_infer_pipeline.py

@@ -129,7 +129,7 @@ class VC(object):
             f0 = f0[0].cpu().numpy()
         elif f0_method == "rmvpe":
             if hasattr(self, "model_rmvpe") == False:
-                from rmvpe import RMVPE
+                from lib.rmvpe import RMVPE
 
                 print("loading rmvpe model")
                 self.model_rmvpe = RMVPE(