io: use clippy to ensure that methods are forwarded in adapters

[Conaclos]

This adds deny(clippy::missing_trait_methods) on impl that must forward calls to the underlying type. This will avoid issues I fixed #705, #703, #701, and #700.

This allowed me to catch a miss.

[Dirbaio]

does it work if you put #![deny(clippy::missing_trait_methods)] at the crate level? this way there's no noise for each impl, and it's not possible to forget to add it on new impls.

[Conaclos]

does it work if you put #![deny(clippy::missing_trait_methods)] at the crate level? this way there's no noise for each impl, and it's not possible to forget to add it on new impls.

Yes. However, it doesn't make sense for some impls, such as Vec and slice, to implement all methods.
I managed to reduce the noise using module-level deny for boxx.rs. I had to separate blanket impl in a dedicated module.

[Dirbaio]

nice!

[Dirbaio]

seems clippy is angry about std impls now

[Conaclos]

seems clippy is angry about std impls now

I always forgot to pass --all-features to Clippy!
It is now fixed. I had to re-add individual deny for the std adapters.