Dm/folder structure

[CodeLieutenant]

Replaced all mod utils; in favour of mod common
to unify the import and remove the magic #[path]
and not rely on it too much (allows copy paste);

Pre-review checklist

• I have split my patch into logically separate commits.
• All commit messages clearly explain what they change and why.
• I added relevant tests for new features and bug fixes.
• All commits compile, pass static checks and pass test.
• PR description sums up the changes and reasons why they should be introduced.
• I have provided docstrings for the public items that I want to introduce.
• I have adjusted the documentation in ./docs/source/.
• I added appropriate Fixes: annotations to PR description.

[github-actions]

cargo semver-checks found no API-breaking changes in this PR! 🎉🥳
Checked commit: a75f79f

[Lorak-mmk]

There is actually no need to edit all the tests.
Remove pub(crate) use utils::*; from scylla/tests/common/mod.rs
Add pub(crate) use common::utils; to scylla/tests/integration/main.rs after mod common;

Then the tests will be able to just import utils mod like before.