chore!: Enable and fix a few pedantic and nursery clippy lints

[sbernauer]

Description

See Cargo.toml on what lints are now enabled. They apply to all workspace members.

Some lints we want to enable in the future, but for now I'm ignoring them, as the PR is big enough already with the easy ones.
E.g. we need to think about many possible number truncations.

I suggest reviewing the commits one by one. Some lints have been auto-corrected (--fix), some manually.

Definition of Done Checklist

• Not all of these items are applicable to all PRs, the author should update this template to only leave the boxes in that are relevant
• Please make sure all these things are done and tick the boxes

Author

• Changes are OpenShift compatible
• CRD changes approved
• CRD documentation for all fields, following the style guide.
• Integration tests passed (for non trivial changes)
• Changes need to be "offline" compatible

Reviewer

• Code contains useful comments
• Code contains useful logging statements
• (Integration-)Test cases added
• Documentation added or updated. Follows the style guide.
• Changelog updated
• Cargo.toml only contains references to git tags (not specific commits or branches)

Acceptance

• Feature Tracker has been updated
• Proper release label has been added