engine: migrate from py3.14-removed 'ast' classes

[jayaddison]

Migrate away from some ast classes that are removed in version 3.14 of Python, as discovered due to continuous integration test failures with prerelease/alpha versions of Py314. The recommended migration path, as followed here, is to replace references to them with ast.Constant instead.

Resolves #224.

[jayaddison]

Hi @jaraco - a small Python π compatibility fixup here for inflect -- I believe it's backwards compatible to all supported runtime Py versions listed by the package (3.9+).

[jaraco]

Merged as 8282d6a.

[jayaddison]

Thanks @jaraco!