Python 3.14 compatibility

[akaihola]

As reported by our future test, the following issues need to be resolved to ensure Python 3.14 compatibility:

• ast class hierarchy changes – upgrade astor, flynt

astor/op_util.py:92: DeprecationWarning: ast.Num is deprecated and will be removed in Python 3.14; use ast.Constant instead
flynt/utils/utils.py:74: DeprecationWarning: ast.Str is deprecated and will be removed in Python 3.14; use ast.Constant instead
flynt/candidates/ast_call_candidates.py:14: DeprecationWarning: ast.Str is deprecated and will be removed in Python 3.14; use ast.Constant instead
flynt/transform/format_call_transforms.py:18: DeprecationWarning: ast.Str is deprecated and will be removed in Python 3.14; use ast.Constant instead
flynt/transform/format_call_transforms.py:22: DeprecationWarning: Attribute s is deprecated and will be removed in Python 3.14; use value instead
flynt/transform/format_call_transforms.py:29: DeprecationWarning: ast.Str is deprecated and will be removed in Python 3.14; use ast.Constant instead
flynt/utils/utils.py:90: DeprecationWarning: ast.Str is deprecated and will be removed in Python 3.14; use ast.Constant instead
flynt/transform/format_call_transforms.py:88: DeprecationWarning: ast.Str is deprecated and will be removed in Python 3.14; use ast.Constant instead
astor/code_gen.py:599: DeprecationWarning: ast.Str is deprecated and will be removed in Python 3.14; use ast.Constant instead
flynt/transform/format_call_transforms.py:89: DeprecationWarning: ast.Str is deprecated and will be removed in Python 3.14; use ast.Constant instead