refactor: decouple IBCStore into a separate contract

[srdtrk]

closes: #71

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.51%. Comparing base (e120d31) to head (bbf070a).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #76   +/-   ##
=======================================
  Coverage   98.51%   98.51%           
=======================================
  Files          12       12           
  Lines         337      337           
  Branches       11       11           
=======================================
  Hits          332      332           
  Misses          5        5           

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[gjermundgaraba]

The code lookgs good. I would be interested to also see updates to the benchmarks, if the cross-contract calls here have any significant impact on gas or not.