Support tox v4 and add action to generate lockfile

[coretl]

At the moment we use tox to:

• Run specific tox envs in CI and locally, like tox -e docs to invoke sphinx with the right args including for autobuild
• Run tox -p to do the tasks that CI will run, but in parallel in a single terminal under a single version of python
• Do this without making a venv for each env with tox-direct

We considered using nox, but it doesn't have a parallel option at the moment as per wntrblm/nox#544

We would like to add the ability to do something like tox -e lock to generate dev-requirements.txt as specified in DiamondLightSource/blueapi#499

To do this we should should update to tox 4 and work out what changes are needed to support the current workflow, and also work out how to add a lock command that will not be run by the equivalent of tox -p

[stan-dot]

for the extra job something like this could work:

# tox must currently be configured via an embedded ini string
# See: https://github.com/tox-dev/tox/issues/999
[tool.tox]
legacy_tox_ini = """
[tox]
skipsdist=True
envlist = pre-commit,type-checking,tests,docs

[testenv:{pre-commit,type-checking,tests,docs}]
# Don't create a virtualenv for the command, requires tox-direct plugin
direct = True
passenv = *
allowlist_externals =
    pytest
    pre-commit
    mypy
    sphinx-build
    sphinx-autobuild
commands =
    pre-commit: pre-commit run --all-files {posargs}
    type-checking: mypy src tests {posargs}
    tests: pytest --cov=blueapi --cov-report term --cov-report xml:cov.xml {posargs}
    docs: sphinx-{posargs:build -EW --keep-going} -T docs build/html

[testenv:custom-job]
direct = True
passenv = *
commands =
    # Replace this line with whatever command this job should run
    echo Running custom job tasks {posargs}
"""

[coretl]

interesting, so does that mean that if you don't add it to the envlist then it won't run when you do tox -p?

[stan-dot]

possibly, will test soon