Unmaintained dependency: backoff

[poljar]

The backoff crate seems to be unmaintained: ihrwein/backoff#66

The issue suggests the backon crate: https://docs.rs/backon/1.2.0/backon/.

backon isn't a drop-in replacement, but it seems to have WASM support, which means we could merge our HttpClient implementations.

[Xuanwo]

Hi, the maintainer of backon here. Let me know if you would like my assistance with the migration.

[poljar]

Ah, thanks for contacting us, we just didn't yet get to it.

One thing I didn't see in the docs is how to handle something like a 429 HTTP error which contains a Retry-After header.

This was added to backoff after a request from our side: ihrwein/backoff#35.

[Xuanwo]

Thank you @poljar for the information, I will take a look.