rust-pyo3: new module for conversions of HgPath and friends Same as `PyRevision`, the `PyHgPathRef` new-type wrapper is not a Python type, but it implements `IntoPyObject`, which will spare us tedious uses of `PyBytes::new`. The `paths_py_list` function is the the analog of `revs_py_list` for paths. There was one similar utility in `hg-cpython`, within the `dirstate::status` module. We feel it should be in a more global location, and have a name consistent with utilities for revisions. The `paths_pyiter_collect` function is similarly the analog of `revs_pyiter_collect`.