Improve eachBatch method

[SebC99]

Currently, what's happening with the eachBatch Query method is this:

• find X objects
• execute a callback on these objects
• find the next X objects
  The issue is that while executing the callback, nothing is done, and we have to wait for the next Find to succeed to start again the callback.

An easy improvement is to launch the next query in parallel of the execution of the callback, so that when the callback is done, the next batch is already ready to be consumed (or more advanced if the query is longer than the callback execution)

It's done by changing the order of the promises, and waiting for both the query and the callback on the previous batch to be resolved.

[SebC99]

I don't know why the tests are failing, I hope it has nothing to do with the modifications...

[SebC99]

Ok so I had to change the way I tested for the end of continueWhile as in the test suite, the find mock doesn't take into account the where clause on the objectId.
Instead of rewriting all the tests for eachBatch, each, map, reduce, and filter I've modified the last call of the promise.

[codecov]

Codecov Report

Merging #1179 into master will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1179   +/-   ##
=======================================
  Coverage   92.21%   92.22%           
=======================================
  Files          54       54           
  Lines        5268     5273    +5     
  Branches     1178     1180    +2     
=======================================
+ Hits         4858     4863    +5     
  Misses        410      410           

Impacted Files	Coverage Δ
src/ParseQuery.js	96.23% <100.00%> (+0.02%)	⬆️

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[SebC99]

(sorry for the force-pushed, I had wrongly pushed another commit with the "built" version I also have)

[dplewis]

Thanks for the improvements. LGTM!

[dplewis]

@SebC99 Sorry for the late reply? Can you rebase your branch?

[SebC99]

Done :)