feat: enable non-`'static` where possible

[Daniel-Bloom-dfinity]

Motivation

Currently, many tower service wrappers and layers are limited to working with 'static types, which limits its usefulness when working with non-statically borrowed things to and from scoped tasks (e.g. async-scoped).

Solution

Remove the 'static restrictions where possible, mostly by introducing lifetime parameters.

This change excludes Buffer and BufferLayer which are more difficult to make non-'static. It is possible to do by abstracting tokio::spawn into a trait (which async_scoped::Scope can also implement), this is also pending the publish of the recently merged tokio-rs/tokio#5665.

[Daniel-Aaron-Bloom]

@GlenDC Yes, it is mildly breaking, so probably has to wait for a minor version. Also I have lost access to the account which made this PR, so you can close it in favor of #765

[tobz]

Closing in favor in #765.