Python 3.14: `AttributeError: module 'ast' has no attribute '_Unparser'`

[hugovk]

refactor no longer works on Python 3.14:

Python 3.14.0 (v3.14.0:ebf955df7a8, Oct  7 2025, 08:20:14) [Clang 16.0.0 (clang-1600.0.26.6)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import refactor
Traceback (most recent call last):
  File "<python-input-0>", line 1, in <module>
    import refactor
  File "/private/tmp/refactor/refactor/__init__.py", line 4, in <module>
    from refactor.actions import *
  File "/private/tmp/refactor/refactor/actions.py", line 9, in <module>
    from refactor.ast import split_lines
  File "/private/tmp/refactor/refactor/ast.py", line 110, in <module>
    class BaseUnparser(ast._Unparser):  # type: ignore
                       ^^^^^^^^^^^^^
AttributeError: module 'ast' has no attribute '_Unparser'. Did you mean: 'unparse'?

3.13 is okay:

Python 3.13.9 (v3.13.9:8183fa5e3f7, Oct 14 2025, 10:27:13) [Clang 16.0.0 (clang-1600.0.26.6)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import refactor
>>>

This also prevents tools such as https://github.com/isidentical/teyit from running on Python 3.14.