rust-cpython: set conversion for MissingAncestors.bases()...
rust-cpython: set conversion for MissingAncestors.bases()
Also I hope that the separate `py_set()` helper will help transition
to proper `PySet` support in `rust-cpython`
Took the opportunity to replace explict for loop with iteration
and collect().
Differential Revision:
https://phab.mercurial-scm.org/D5581