Rust makes it hard to create blanket trait impls

[teor2345]

This impacts interop tools, but also Rust frameworks like Bevy.

Specifically:

• it is easy for blanket impls to overlap, cause other code to be ambiguous, or other impls to overlap
• it is hard to create mutually exclusive blanket impls for categories of types, but there are workarounds
• specialisation isn't stable, and the workarounds aren't ergonomic
• there is a lot of boilerplate code involved, particularly in some workarounds

Background:

• https://patterns.contextgeneric.dev/blanket-implementations.html
• https://geo-ant.github.io/blog/2021/mutually-exclusive-traits-rust/
• https://stackoverflow.com/questions/73782573/why-do-blanket-implementations-for-two-different-traits-conflict
• https://internals.rust-lang.org/t/blanket-implementation-for-impl-t-u-into-t-into-option-t-for-option-u/19442/6
• https://internals.rust-lang.org/t/impl-t-u-from-t-from-vec-t-for-vec-u/19116