feat: support retry function

[jenjen75]

Hello,

ofetch and all unjs package are really awesome !

So far, retry option allow number which retry fetch until the count is 0.
This PR allow to set retry with a function. It can be useful to handle programmatically or delay retries, it allow to implement any retry backoff algorithm.

[codecov]

Codecov Report

Merging #253 (543da56) into main (41c3b56) will decrease coverage by 0.55%.
The diff coverage is 50.00%.

@@            Coverage Diff             @@
##             main     #253      +/-   ##
==========================================
- Coverage   90.47%   89.93%   -0.55%     
==========================================
  Files           5        5              
  Lines         462      467       +5     
  Branches       74       76       +2     
==========================================
+ Hits          418      420       +2     
- Misses         44       47       +3     

Impacted Files	Coverage Δ
src/fetch.ts	93.49% <50.00%> (-1.11%)	⬇️

[zweeen]

@jenjen75 thank you very much for this feature can you improve your code to take into account the Codecov Report please.

[pi0]

Hi dear @jenjen75 thanks so much for making this PR and sorry it took long to respond ❤️

I think with the addition of retryDelay in #262 and using interceptors it should be possible to conditionally/progreammatically have different behaviors.

I am little bit hesitated to introduce this feature because it adds little bit to the bundle size.

But i am happy to reopen and discuss if you think differently 👍🏼