Replace `black` with `ruff` and add `pre-commit`

[davidwilby]

Hey @tom-andersson et al - just a maintenance-related PR for your perusal, feel free to reject if this isn't your thing.

What this PR does

• resolves #109
• replaces black with ruff as the linter of choice, partially because of extra features such as linting docstrings in google-style (which black may do as well, but I haven't been able to find it)
• adds pre-commit and a pre-commit config to run the ruff linter and formatter on a pre-commit hook.
• adds info to CONTRIBUTING.md detailing the use of these tools.

What this PR doesn't do

• actually formatting the codebase with ruff so far in this branch to avoid the massive diff
• add a pull request template to remind contributors to follow these steps (that will follow in another PR)

At the moment the CI check fails since ruff is checking all the docstrings, we may be able to soften the docstring rules (configured in pyproject.toml) to something we agree with (e.g. I don't necessarily think that every module needs a docstring)

FYI @nilsleh

[tom-andersson]

Thank you @davidwilby, this does look quite useful. I checked the error message of the CI and we now get many failing docstring checks. Can you 1) address the simpler syntax ones 2) silence more complex issues like missing public function docstrings, so that tests pass?

It looks like we can ignore error messages in pyproject.toml with:

[tool.ruff.lint]

ignore = [
    # Relax the convention by _not_ requiring documentation for every function parameter.
    "D417",
]

[davidwilby]

@tom-andersson I've added a number of rules to ignore and performed the remaining linting of docstrings (the code itself was completely compliant from using black)

The remaining linting failures are for missing docstrings on public methods/functions:

deepsensor/data/loader.py:809:9: D102 Missing docstring in public method
deepsensor/data/task.py:32:9: D102 Missing docstring in public method
deepsensor/model/convnp.py:446:9: D102 Missing docstring in public method
deepsensor/model/convnp.py:469:9: D102 Missing docstring in public method
deepsensor/model/convnp.py:492:9: D102 Missing docstring in public method
deepsensor/model/convnp.py:517:9: D102 Missing docstring in public method
deepsensor/model/convnp.py:553:9: D102 Missing docstring in public method
deepsensor/model/convnp.py:588:9: D102 Missing docstring in public method
deepsensor/model/convnp.py:620:9: D102 Missing docstring in public method
deepsensor/model/convnp.py:638:9: D102 Missing docstring in public method
deepsensor/model/convnp.py:977:5: D103 Missing docstring in public function
deepsensor/model/model.py:84:9: D102 Missing docstring in public method
deepsensor/model/model.py:612:5: D103 Missing docstring in public function
deepsensor/tensorflow/__init__.py:19:5: D103 Missing docstring in public function
deepsensor/torch/__init__.py:19:5: D103 Missing docstring in public function
deepsensor/train/train.py:168:9: D102 Missing docstring in public method

I've had a go at adding a few missing docstrings in 678602a but other than that I don't know enough to write them.

One option (which I've used in a couple of places) is to add a # noqa tag for functions/methods that aren't really meant for public usage.

Could you add some docstrings or advise on those that are remaining when you get the chance?