Add `Clone`, `Copy` & `Debug` to `PrinterOptions`

I'd love to see Clone, Copy and Debug implemented for PrinterOptions<'a>.
Especially the first one - it would be very nice to quickly re-use the same options between different to_css invocations.

Clone & Copy

As far as I understand, the main reason this is not implemented, is source_map that is passed as mutable reference. That indeed
prevents us from cloning the printer.

However, note, that this field is behind sourcemap feature. Therefore I would recommend adding:

#[cfg_attr(not(feature = "source map"), derive(Clone, Copy))]

Debug

I don't see a reason why this is not implemented. I guess it was never needed but it is a nice QoL improvement.

Other structures

Other structures would also need the change - at least DependencyOptions and PseudoClasses. It seems that Targets already implements all three traits.

I'd love to create a PR with those improvements.

Locate PrinterOptions, DependencyOptions, PseudoClasses, and Targets, then compare the trait implementations already present on Targets. Check how the source_map feature affects PrinterOptions and verify that the requested Clone, Copy, and Debug implementations are consistent across these structures.