Ease plugin hook restrictions

[JonasKruckenberg]

What kind of change does this PR introduce?

• Bugfix
• Feature
• Docs
• New Binding issue #___
• Code style update
• Refactor
• Build-related changes
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Does this PR introduce a breaking change?

• Yes, and the changes were approved in issue #___
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Checklist

• When resolving issues, they are referenced in the PR's title (e.g fix: remove a typo, closes #___, #___)
• A change file is added if any packages will require a version bump due to this PR per the instructions in the readme.
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Other information

Relaxes the Sync Requirement for plugin callbacks and allows FnMut callbacks as the setup hook.
Ideally we should make this FnOnce as the setup hook must only ever be called once anyway, but I haven't found a nice way to do so yet (Can one take a value out of a trait object? Can we call the fn and replace it's memory somehow?)

[lucasfernog]

@JonasKruckenberg can you fix fmt here

[JonasKruckenberg]

done