[Feature]: Add starting power offset for the exponential backoff

### What problem are you facing?

Hi guys!
I've noticed that your implementation of the exponential backoff is returning a delay of : `0.5`, `1`, `2`, `4`s...

Would it be possible to have a way to provide a custom retry implementation along with the one that you provide? or, as a simpler change, add another parameter to let us decide the initial power parameter? For my use case, I'd need my retries to be performed after 2s, 4s and 8s.
So I was thinking about something like `.exponential(base: 2, from: 1)` or `.exponential(base: 2, skip: 2)` ..

What do you think ?

### Other Information

_No response_

Start by locating the existing exponential backoff implementation and its tests. Review how the current 0.5, 1, 2, and 4 second delays are calculated, then determine how an offset such as from: 1 should produce 2, 4, and 8 second retries. Done means the offset is configurable and existing behavior remains covered by tests.

Written by the indexing model from the issue text.