Cleanup testsuite

[stormshield-gt]

Cleanup the further the testsuite by doing the following:

• Remove assert!(result.is_ok()) pattern, which gives less context in case of failure than result.unwrap()
• Move the example of the README directly inside the lib.rs to compile them. Fix some examples that silently didn't compile until then.
• Fix doc generation warning and add a ci check for it
• Detect slow test with cargo +nightly t --workspace -- -Z unstable-options --report-time --format json 2> /dev/null | jq and ignore them locally. This improves the developer experience.
• Update README to new test location since testscontainers migration

I split the PR into several commits to ease the review.

[stormshield-gt]

Hi @Haennetz, happy new year!
Just a friendly ping; Do you think you will have some bandwidth soon to review this soon?

[Haennetz]

Happy new year 🎉🎊
I will review it until Sunday.

[Haennetz]

Really nice work 👍