Use the ParIterator in GroupReadsByUmi

[nh13]

@tfenne I tried updating the code to use the new ParIterator (and it also now skips sorting if the input is template-coordinate), but it seems to be all IO bound, so not sure either are worth it. Perhaps I change the PR to only keep the sorting skip. Can you take a look/run on your end?

[codecov-commenter]

Codecov Report

Merging #791 (ed2ef78) into feature/group-reads-by-umi-threading (544b256) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@                          Coverage Diff                          @@
##           feature/group-reads-by-umi-threading     #791   +/-   ##
=====================================================================
  Coverage                                 95.46%   95.47%           
=====================================================================
  Files                                       121      121           
  Lines                                      6864     6867    +3     
  Branches                                    453      465   +12     
=====================================================================
+ Hits                                       6553     6556    +3     
  Misses                                      311      311           

Flag	Coverage Δ
unittests	95.47% <100.00%> (+<0.01%)	⬆️

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Impacted Files	Coverage Δ
...cala/com/fulcrumgenomics/umi/GroupReadsByUmi.scala	94.27% <100.00%> (+0.07%)	⬆️

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