Refactor Statistics submodule

[nikml]

• Remove copy operations for SizeBasedChunking and use iloc instead of loc
• Remove copy operations from Base Calculator/Estimator
• Refactored statistics calculators to more efficiently calculate
• Added tests to all calculators to ensure reference/analysis data are not changed after using a calculator since we are removing expensive copy operations

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 76.73%. Comparing base (da33807) to head (cc869eb).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #390      +/-   ##
==========================================
+ Coverage   76.52%   76.73%   +0.21%     
==========================================
  Files         110      109       -1     
  Lines        9242     9250       +8     
  Branches     1658     1658              
==========================================
+ Hits         7072     7098      +26     
+ Misses       1703     1686      -17     
+ Partials      467      466       -1     

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