Custom Backoff for Eventually Family of Functions

[Akaame]

https://github.com/Akaame/testify/pull/1/changes

I have an idea here to provide custom backoff timers for the Eventually call instead of having a set linear backoff at the interface. After 15 minutes of sketching, I think, we could introduce a EventuallyWithBackoff to avoid any breaking changes.

This is not a breaking change but an additive one as any breaking changes to v1 are TOTALLY discouraged. If there is any interest on this or if the maintainers are positive on such a change, I would like to spend some time on it and expand the solution to more mature and encompassing one. If the base idea is out of scope of this library, we can just close the discussion.

Looking forward to your feedback on if the idea is worth working on.

Cheers 🍺