Deprecation warning from ast

[mgao6767]

Describe the bug
Some deprecation warnings from ast.

Additional context
The following that appear in the code have been deprecated and will be deleted in Python 3.14.

• ast.Ellipsis
• ast.Num
• ast.NameConstant
• ast.Str
  These can be replaced with ast.Constant.

In addition,

xian-contracting/src/contracting/compilation/compiler.py

Line 118 in d8fd3cf

def visit_Num(self, node):

should be visit_Constant instead. Also, node.n should be replaced by node.value.