ci: use clippy; abort run on failure

[w-lfchen]

Description

current state:

• clippy is installed in ci but never invoked
• cargo check is executed to check for warnings, but no actionis taken if some exist.

this pr changes both of these things.
clippy is used and if there is a warning or a lint, ci fails.

Additional Notes

• ci should fail for the first commit, i'll push a fix once that happened (worked as expected).
• it might be worth splitting up things in the workflows so that they can run in parallel.
• i am against ci modifying code.
• i might look into applying some changes from Add Test runs to CI, don't run gh-pages from forks #590

Checklist

• I added my changes to CHANGELOG.md, if appropriate.
  i don't think this applies here
• I used cargo fmt to automatically format all code before committing

[w-lfchen]

this is needed to fail ci, see the clippy ci docs