#[derive(PyEnum)] procedural macro.
This is the entry-point crate. Parsing, validation, and codegen live in
the submodules and are wired together by [derive_pyenum] below. The
generated code references only items re-exported from pyenum::__private
so the output is feature-flag-free — the runtime crate's compat module
resolves those names per the active pyo3-0_XX feature.