Add #[derive(Debug)] to relevant structs for easier debugging

[giftedoddd]

Hi,
First off, thank you for all the work you've put into lofty-rs.
I'd like to suggest adding the #[derive(Debug)] attribute to more of the In particular, structs like TaggedFile, Tag, or other core types in the crate. This would greatly help during development and debugging, as it allows developers to quickly inspect the contents of structs.
It would improve the developer experience without changing any functionality.