Improve performance by grouping and limiting via DB queries

[btschwertfeger]

Summary

• Adding and improving comments
• Making use of limiting and ordering orders from the orderbook

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.35%. Comparing base (a293bdc) to head (6c2f4d3).

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #65      +/-   ##
==========================================
+ Coverage   85.10%   85.35%   +0.24%     
==========================================
  Files           6        6              
  Lines         920      922       +2     
==========================================
+ Hits          783      787       +4     
+ Misses        137      135       -2     

Flag	Coverage Δ
unittests	85.35% <100.00%> (+0.24%)	⬆️

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Files with missing lines	Coverage Δ
src/kraken_infinity_grid/database.py	84.65% <100.00%> (+0.67%)	⬆️
src/kraken_infinity_grid/gridbot.py	70.99% <100.00%> (ø)
src/kraken_infinity_grid/order_management.py	92.00% <100.00%> (+0.59%)	⬆️
src/kraken_infinity_grid/setup.py	98.92% <ø> (ø)