fix druid connector with tests

[cosmic-chichu]

• decouple method to increase testability
• remove extraneous subquery

[codecov[bot]]

Codecov Report

Merging #296 (84e0023) into main (98e376a) will increase coverage by 0.00%. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #296   +/-   ##
=======================================
  Coverage   93.82%   93.83%           
=======================================
  Files          74       74           
  Lines        3386     3390    +4     
  Branches      277      276    -1     
=======================================
+ Hits         3177     3181    +4     
  Misses        157      157           
  Partials       52       52           

Files Changed	Coverage Δ
numalogic/connectors/druid.py	87.50% <100.00%> (+1.13%)	:arrow_up:

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