refactor(retry.sleepDuration): ♻️ extract jitterBackoff function

[ninedraft]

Refactor sleepDuration function and use local random generatpr

[codecov]

Codecov Report

Merging #406 (621a643) into master (61f4307) will increase coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #406      +/-   ##
==========================================
+ Coverage   95.97%   96.01%   +0.03%     
==========================================
  Files          10       10              
  Lines        1019     1029      +10     
==========================================
+ Hits          978      988      +10     
  Misses         23       23              
  Partials       18       18              

Impacted Files	Coverage Δ
retry.go	100.00% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 61f4307...621a643. Read the comment docs.

[ninedraft]

@jeevatkm if you are not going to take this MR, please write. This will not offend me at all, I will just try to look for other places in your project where I could be useful!

[jeevatkm]

Hello @ninedraft it's not like that. I really appreciate your contribution. Lately, I have been busy with a couple of projects in my day jobs. I'm not getting enough time. In the upcoming days, it will be alright. I will look at this PR this week. Thanks again!

[jeevatkm]

@ninedraft Thanks for your PR and improving Resty.
I'm really sorry for the delay, due to personal reasons.

[ninedraft]

thx!