Deprecation warnings due to deprecated features in the ast module

[flyersworder]

Can we do the updates accordingly to ensure this library still works after Python 3.14? Many thanks.

DeprecationWarning: ast.Num is deprecated and will be removed in Python 3.14; use ast.Constant instead
DeprecationWarning: ast.Str is deprecated and will be removed in Python 3.14; use ast.Constant instead
DeprecationWarning: Attribute s is deprecated and will be removed in Python 3.14; use value instead

[berkerpeksag]

Thanks for the report. This is a duplicate of #217. astor 0.9 (PR #229) will fix all deprecation warnings.