Introduce ruff as a Python linter (#82)

The `ruff` linter has support for checks that some of our existing
linters don't, most notably the ability to detect (and fix, if
requested) unused imports. Unused imports are a cause of [many PR
comments](reboot-dev/mono#2159) and wasted
time.

`ruff` is also a code formatter, but there's currently no strong reason
to switch from `yapf` to `ruff` for that in our codebase.

check-code-style/action.yml

@@ -59,7 +59,8 @@ runs:
         pip install \
           yapf==0.33.0 \
           mypy==1.2.0 \
-          isort==5.12.0
+          isort==5.12.0 \
+          ruff==0.1.14
       shell: bash
 
     - name: Run code style checks on all code.

check-style.sh

@@ -120,6 +120,9 @@ if [ ! -z "${python_files}" ]; then
     # Run yapf.
     run_check yapf -d -p ${python_files}
 
+    # Run ruff.
+    run_check ruff check ${python_files}
+
     # Run isort
     run_check isort --check --diff ${python_files}
 fi