Fix ruff 0.16 compatibility (pin default rule set + concise output)

[dchaudhari7177]

Fixes #69.

Ruff 0.16 broke test_ruff_ok, test_ruff_error, and test_ruff_config with two independent changes:

1. New rules in the default set. Ruff 0.16 promoted I (isort) and FA (flake8-future-annotations) into its default rule selection. Since ruff_config() used --extend-select on top of ruff's defaults, examples suddenly got I001 / FA100 that pytest-examples never opted into (import sorting is opt-in via isort=, and there's no future-annotations option at all).

   Fix: pin ruff's classic default base (E4,E7,E9,F) explicitly and use --select, so the enforced rule set no longer drifts with ruff's defaults. Opt-in flags (isort, upgrade, quotes, ruff_select) extend this base exactly as before. This reproduces the pre-0.16 behavior, so the existing test assertions pass unchanged.

2. Default output format changed. Ruff 0.16 made the grouped full format the default, which breaks the ^-:(\d+) offset rewriting in ruff_check and the readable one-error-per-line output. Fix: pass --output-format=concise explicitly.

tests/test_lint.py and the ruff/isort/upgrade cases in tests/test_run_examples.py are green.

Out of scope: a few test_black_* / test_insert_print cases and test_update_examples_dir.py also fail on main, but those are due to a newer black/pytest, not ruff — happy to tackle them separately if useful.