CPython's PySequence_Contains (Objects/abstract.c::_PySequence_IterSearch)
catches the TypeError from PyObject_GetIter when neither __contains__ nor
__iter__ is available, and re-raises with membership-test wording.
RustPython's PySequence::contains propagated the get_iter error verbatim,
so '1 in obj' produced 'X' object is not iterable — a literal but less
specific message.
Wrap the get_iter call in map_err: when the failure is a TypeError,
re-raise with byte-identical CPython wording. Other exception types pass
through unchanged.
Unmasks test_contains.TestContains.test_common_tests.
Changjoon