feat: add exponential backoff and retries for push/send

[wschurman]

Why

We'll be adding rate limiting to the push/send API soon, so before that it'd be good to have this library handle 429s gracefully.

How

Add promise-retry with 2 retries and exponential backoff.

Test Plan

Run unit test.

[codecov]

Codecov Report

Merging #52 (d1dac81) into master (0205b91) will decrease coverage by 0.57%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #52      +/-   ##
==========================================
- Coverage   99.35%   98.77%   -0.58%     
==========================================
  Files           1        1              
  Lines         154      163       +9     
  Branches       28       29       +1     
==========================================
+ Hits          153      161       +8     
  Misses          1        1              
- Partials        0        1       +1     

Flag	Coverage Δ
node_10_x	98.77% <100.00%> (-0.58%)	⬇️
node_12_x	98.77% <100.00%> (-0.58%)	⬇️
node_14_x	98.77% <100.00%> (-0.58%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/ExpoClient.ts	98.77% <100.00%> (-0.58%)	⬇️

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[wschurman]

The addition of promiseRetry means that the promiseLimit is no longer the first awaited call, so this test is no longer reliable.

[wschurman]

Noted inline about why promiseRetry is difficult (maybe impossible) to test in an asynchronous context with jest mock timers. I had a few other ideas, but it seems unlikely that any of them will pan out:

• mock setTimeout with custom implementation (don't think this is possible?)

[wschurman]

I was unable to get the mock timers to work unfortunately. That being said, these seem to finish in under the default timeout, so I'm not too worried.

[ide]

My primary concern is human time, not CI time. The unit tests are actually "fast, reliable tests" that should give feedback as fast as possible, so we never want to wait for timers with them. Another reasonable solution would be to make it so that the backoff in tests is always 0ms.