feat: optimize VyperNode.__deepcopy__ (vyperlang#3784)

`VyperNode.__deepcopy__` is a hotspot in the frontend. this commit
improves time spent in the frontend by 10%

vyper/ast/nodes.py

@@ -4,6 +4,7 @@
 import decimal
 import functools
 import operator
+import pickle
 import sys
 import warnings
 from typing import Any, Optional, Union
@@ -357,6 +358,9 @@ def __hash__(self):
         values = [getattr(self, i, None) for i in VyperNode.__slots__ if not i.startswith("_")]
         return hash(tuple(values))
 
+    def __deepcopy__(self, memo):
+        return pickle.loads(pickle.dumps(self))
+
     def __eq__(self, other):
         if not isinstance(other, type(self)):
             return False
@@ -786,7 +790,6 @@ class ExprNode(VyperNode):
 
     def __init__(self, *args, **kwargs):
         super().__init__(*args, **kwargs)
-
         self._expr_info = None