tests: port test-hybridencode.py to unittest
This was done predominantly through keyboard macros in emacs, so it's
not always pretty, but it's enough to make the test easier to work
with. There's a ton of room for improvement in this file, but it would
be labor intensive and error-prone, so I went with the dumbest option
that could work, so as to avoid transcription errors.
Paranoia:
$ egrep '^ def test' tests/test-hybridencode.py | wc -l
44
$ egrep '^ def test' tests/test-hybridencode.py | sort | uniq | wc -l
so I'm pretty confident there aren't any shadowed test methods.
This fixes the test on Python 3.
Differential Revision: https://phab.mercurial-scm.org/D3466