Move lists to maps

[codecov[bot]]

Codecov Report

Merging #188 (54ed6b5) into implement_send_request (4e848ea) will increase coverage by 0.20%. The diff coverage is 91.30%.

@@                    Coverage Diff                     @@
##           implement_send_request     #188      +/-   ##
==========================================================
+ Coverage                   92.11%   92.32%   +0.20%     
==========================================================
  Files                          10       10              
  Lines                         444      443       -1     
==========================================================
  Hits                          409      409              
+ Misses                         35       34       -1     

Impacted Files	Coverage Δ
src/wpool_queue_manager.erl	87.64% <50.00%> (+0.82%)	:arrow_up:
src/wpool.erl	97.22% <100.00%> (-0.08%)	:arrow_down:
src/wpool_process.erl	80.76% <100.00%> (+0.24%)	:arrow_up:
src/wpool_process_callbacks.erl	89.47% <100.00%> (-0.53%)	:arrow_down:
src/wpool_utils.erl	100.00% <100.00%> (ø)

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[elbrujohalcon]

This looks good.