Formatting follow up

[andhus]

Thanks for the work in https://github.com/andhus/dirhash-python/pull/26 @frichtarik 🙏

I condensed it a bit here according to my preferences, mainly:

• replaces black, isort and flake8 with ruff and ruff-format
• breaks out pre-commit in tox.ini and runs it in a separate job (for clarity)
• removes auto commit (was not running if the previous step failed, and mainly only works for the main fork and I won't use it)

I appreciate any feedback/questions.

(I can apply similar changes after emerging your corresponding fixes in https://github.com/andhus/scantree/pull/21)

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 100.00%. Comparing base (5109248) to head (7b2aad3).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #27 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 2 2 Lines 194 194 Branches 34 34 ========================================= Hits 194 194 ```

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