copies: introduce the hg-cpython wrapper for `combine_changeset_copies` This patch focus on the `hg-cpython` part of this work. Bridging the python code with the new rust code in `hg-core`. The next patch will actually plug this in the python code. The rust code use multiple Python callback, python related error within this callback are not expected unless they are a programming error or a data corruption. In addition, these callback will slowly be replaced by native Rust code. For these reasons, we use will deal with unexpected error within this callback using rust Panic and let the `rust-cpython` layer deal with raising a Python exception. The code dealing with the ChangedFile instance is repeating itself a lot. I did not factor these duplication out because that whole code will get replaced by entirely different one in a handful of changesets. Differential Revision: https://phab.mercurial-scm.org/D9298

copies: introduce a basic Rust function for `combine_changeset_copies` This new function mirror the python code. This first implementation does a lot of data copies and is therefore quite slow. However my goal here is to create a simple "frame" from where to start adding optimization. This patch focus on the `hg-core` part of this work. Coming patches will do the necessary `hg-cpython` work to be able to use this from Python. Differential Revision: https://phab.mercurial-scm.org/D9297

hghave: adjust the detection of `pylint` for modern versions I have pylint 2.6.0 installed locally, and it only has a single space. I have no idea when this changed. Differential Revision: https://phab.mercurial-scm.org/D9431

formating: upgrade to black 20.8b1 This required a couple of small tweaks to un-confuse black, but now it works. Big formatting changes come from: * Dramatically improved collection-splitting logic upstream * Black having a strong (correct IMO) opinion that """ is better than ''' Differential Revision: https://phab.mercurial-scm.org/D9430

osutil: reformat triple-quoted string so black doesn't confuse itself Differential Revision: https://phab.mercurial-scm.org/D9429

merge: remove spurious ' and trailing whitespace from triple-quoted string Differential Revision: https://phab.mercurial-scm.org/D9428

cleanup: fix a few recent black formatting violations Differential Revision: https://phab.mercurial-scm.org/D9427