Add pre-commit configuration and workflow

Add a pre-commit [1] configuration in `.pre-commit-config.yaml` and a
corresponding GitHub workflow to run the checks on pull requests.

The pre-commit checks use ruff [2] for both linting and formatting.
Developers should integrate these checks into their local workflow by
installing pre-commit and running `pre-commit install` to enable the local
pre-commit hook.

Note that we have removed `tox -e pep8` from the existing test workflow, since
there's no reason to run the linting as part of the Python version matrix.

[1]: https://pre-commit.com/
[2]: https://docs.astral.sh/ruff/

.github/workflows/precommit.yaml

@@ -0,0 +1,31 @@
+name: Run pre-commit checks
+
+on:
+  pull_request:
+  push:
+
+jobs:
+  run-linters:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check out code
+        uses: actions/checkout@v4
+
+      - name: Setup Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.x"
+
+      - name: Configure caching
+        uses: actions/cache@v4
+        with:
+          path: ~/.cache/pre-commit
+          key: precommit-${{ runner.os }}-${{ hashFiles('.pre-commit-config.yaml') }}
+
+      - name: Install pre-commit
+        run: |
+          pip install pre-commit
+
+      - name: Run linters
+        run: |
+          pre-commit run --all-files

.github/workflows/tests.yml → .github/workflows/unit-tests.yaml

@@ -20,7 +20,5 @@ jobs:
         run: |
           python -m pip install --upgrade pip
           pip install tox
-      - name: Lint
-        run: tox -epep8
       - name: Unit Tests
         run: tox -epy3

.pre-commit-config.yaml

@@ -0,0 +1,24 @@
+repos:
+  - repo: https://github.com/Lucas-C/pre-commit-hooks
+    rev: v1.5.5
+    hooks:
+      - id: remove-tabs
+
+  - repo: https://github.com/pre-commit/pre-commit-hooks
+    rev: v4.6.0
+    hooks:
+      - id: trailing-whitespace
+      - id: check-merge-conflict
+      - id: end-of-file-fixer
+      - id: check-added-large-files
+      - id: check-case-conflict
+      - id: detect-private-key
+      - id: check-yaml
+        args: [--allow-multiple-documents]
+
+  - repo: https://github.com/astral-sh/ruff-pre-commit
+    rev: v0.5.1
+    hooks:
+      - id: ruff
+        args: [ --fix ]
+      - id: ruff-format