remove backoff usage

[j-mendez]

Backoff has an infinite loop that can occur with timers that will keep using std::thread::sleep forever when being used with tokio.

[64bit]

proof?

[tkoeppen]

backoff is unmaintained since a while (last release Dec 2021 and no commits since then) [1]

Replace by backon or refactor and remove dependency? [2]

Ref:
[1] ihrwein/backoff#66
[2] https://github.com/Xuanwo/backon