Macro define_stub_info_gatherer

macro_rules! define_stub_info_gatherer {
    ($function_name:ident) => { ... };
}

Create a function to initialize StubInfo from pyproject.toml in CARGO_MANIFEST_DIR.

If pyproject.toml is in another place, you need to create a function to call StubInfo::from_pyproject_toml manually. This must be placed in your PyO3 library crate, i.e. same crate where inventory::submitted, not in gen_stub executables due to inventory mechanism.