Add test requirements to Pipfile[.lock] & bump deps (#2436)

While this development environment / requirements situation is a mess,
let's at least make it consistent. We're effectively supporting two
modes of development in this project, 1) tox based dev commands
(e.g. `tox -e fuzz`) that are dead simple to use, and 2) manual dev
commands (e.g. `pytest -n auto`) that give more control and are usually
faster.

Right now the Pipfile.lock based development environment is incomplete
missing the test requirements specified in ./test_requirements.txt.
This is annoying since manual test commands (e.g. `pytest -k fmtonoff`)
fail. Let's fix this by making Pipfile.lock basically a
"everything you need" requirements file (fuzzing not included since
running it locally is not something common).

Oh and let's bump some documentation deps (and bring some requirements
across .pre-commit-config.yaml, Pipfile, and docs/requirement.txt in
alignment again). Don't worry, I tested these changes so they should
be fine (hopefully!).