Add mypy pre-commit hook

[lewisjared]

Description

Adds pre-commit hook for mypy

Checklist

Please confirm that this pull request has done the following:

• Tests added
• Documentation added (where applicable)
• Changelog item added to changelog/

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

[lewisjared]

Closes #50

[bouweandela]

Since mypy is now run using pre-commit, this job could be removed, right?

cmip-ref/.github/workflows/ci.yaml

Lines 10 to 18 in 8515dbf

	mypy:
	if: ${{ !github.event.pull_request.draft }}
	runs-on: ubuntu-latest
	steps:
	- name: Check out repository
	uses: actions/checkout@v4
	- uses: ./.github/actions/setup
	- name: mypy
	run: make mypy

Could we also run the pre-commit hooks on draft pull requests, so I have a bit more confidence that what I'm doing is up to standards even when it's not yet ready for review? I.e. take out this line?

cmip-ref/.github/workflows/ci.yaml

Line 21 in 8515dbf

if: ${{ !github.event.pull_request.draft }}

Unrelated, but in the same file: since we have the readthedocs build enabled for pull requests, we don't need this action anymore either, do we?

cmip-ref/.github/workflows/ci.yaml

Lines 30 to 46 in 8515dbf

	docs:
	if: ${{ !github.event.pull_request.draft }}
	runs-on: ubuntu-latest
	env:
	REF_DATA_ROOT: ${{ github.workspace }}/tests/test-data/sample-data
	REF_OUTPUT_ROOT: ${{ github.workspace }}/out
	REF_DATABASE_URL: "sqlite:///${{ github.workspace }}/.ref/db/ref.db"
	steps:
	- name: Check out repository
	uses: actions/checkout@v4
	- uses: ./.github/actions/setup
	- name: docs
	run: |
	mkdir -p ${{ github.workspace }}/.ref/db
	make fetch-test-data
	uv run ref datasets ingest --source-type cmip6 $REF_DATA_ROOT
	uv run mkdocs build --strict