rust-cpython: consistency in use of hg-core constructs
While not everybody likes the `CoreLazy` and `CoreIterator`
aliases, it's better not to mix them with direct references.
Note: it's quite possible in the future that these would stop
being exposed at the top of the `hg` crate
Differential Revision: https://phab.mercurial-scm.org/D5547
public attribute not declared in interfaces: badpeer.badattribute
public attribute not declared in interfaces: badpeer.badmethod