req: Encode/Decode for std::ops::Bound<T>

[cornmonger]

Useful for passing range mechanics around.

Low priority, but possibly low hanging fruit as well (it was easy to one-off it).

https://github.com/rust-lang/rust/blob/bf063f193b6fa5d0501884ffad75952ddf7e7b3c/library/core/src/ops/range.rs#L704