Migrate to ruff (#475)

* Switched from flakeheaven to ruff as linter

* Changed docs to now use ruff instead of flakeheaven

* Skip other jobs in CI (revert once change is finished)

* Corrected linting error about not chaning exceptions (B904)

* Corrected linting error about assigning names to lambdas (E731)

* Corrected issue with true-fals-comparisons

* Corrected tests if not member (E713)

* Corrected accessing attributes without assigning them (B018)

* Readded all Tests from CI

* Corrected empty lines with whitespaces (W293)

* Removed trailing whitespaces (W291)

* Corrected comparison to None (E711)

* Forgot to add linebreaks when corrected lambdas