rust: update the rust-cpython crate to 0.7.0 This notably brings support for Python 3.10, and includes the panic message when propagating a Rust panic as a Python exception. https://github.com/dgrunwald/rust-cpython/blob/master/CHANGELOG.md#070---2021-10-09 Differential Revision: https://phab.mercurial-scm.org/D11630