fix: remove CellRange, SlickRange, SlickGroup, ... unused interfaces

[ghiscoding]

• since we moved SlickGrid inside the project, we can now use the TS classes directly instead of relying on similar interfaces
• also remove slick core re-export and replace it by exporting core folder

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (d723856) 86.11% compared to head (c7e5786) 86.11%.

Additional details and impacted files

@@           Coverage Diff           @@
##             next    #1219   +/-   ##
=======================================
  Coverage   86.11%   86.11%           
=======================================
  Files         208      208           
  Lines       21239    21239           
  Branches     7063     7063           
=======================================
  Hits        18287    18287           
  Misses       2952     2952           

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