Derive `newtype` instances where possible

[triallax]

Description of the change

Derive newtype instances instead of "normal" instances where possible, which produces smaller code.

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Checklist:

• [x] Added the change to the changelog's "Unreleased" section with a reference to this PR (e.g. "- Made a change (#0000)")
• [x] Linked any existing issues or proposals that this pull request should close
• [x] Updated or added relevant documentation
• [x] Added a test for the contribution (if applicable)