rust-pyo3: implementation of LazyAncestors There is a difference in the implementaion of `__contains__` between PyO3 and rust-cpython: if the specified signature in Rust code is for a precise type (e.g., `PyRevision`) rust-cpython would automatically convert the potential resulting `TypeError` into `Ok(false)`, whereas PyO3 let it bubble up. Hence we treat the case manually and add it to the common test. In Mercurial Python code, `None in` for a `LazyAncestors` object can really happens, namely in this lambda from `discover._postprocessobsolete`: ``` ispushed = lambda n: torev(n) in futurecommon ``` This lambda can get called with `n` such that `torev(n)` is `False` (seen in `test-bookmarks-push-pull.t`).