formatting: blacken the codebase
This is using my patch to black
(https://github.com/psf/black/pull/826) so we don't un-wrap collection
literals.
Done with:
hg files 'set:**.py - mercurial/thirdparty/** - "contrib/python-zstandard/**"' | xargs black -S
# skip-blame mass-reformatting only
# no-check-commit reformats foo_bar functions
Differential Revision: https://phab.mercurial-scm.org/D6971
ERROR: FIXME: This is a known failure of filelog.size for data starting with \1\n
OK.