Add ruff checks to CI

Mark example-only variables as intentionally unused so ruff can check
the script without changing its illustrative structure.

Change `ruff.lint.select` to `ruff.lint.extend-select` to enable default
lints and fix ambiguous variable name warnings.

Enable import sorting and use `ruff check --fix` to fix existing
violations.

Configure ruff to skip submodules.

Signed-off-by: Tamir Duberstein <tamird@kernel.org>
Link: https://patch.msgid.link/20260419-ruff-check-v2-2-089dfb264501@kernel.org
Signed-off-by: Konstantin Ryabitsev <konstantin@linuxfoundation.org>