Moving statistics calculations to hstats()

[mayer79]

The aim of this PR is to move the calculation of H-statistics into hstats(). This is different from the current implementation where the functions h2(), ... would take an "hstats" object and do the cheap calculations themselfes. These functions should only care about postprocessing, like "take square?", "normalize", etc.

[codecov-commenter]

Codecov Report

Patch coverage: 100.00% and project coverage change: -0.01% ⚠️

Comparison is base (d7001dd) 97.81% compared to head (5a5faa7) 97.80%.

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Additional details and impacted files

@@            Coverage Diff             @@
##             main      #61      +/-   ##
==========================================
- Coverage   97.81%   97.80%   -0.01%     
==========================================
  Files          14       14              
  Lines         732      730       -2     
==========================================
- Hits          716      714       -2     
  Misses         16       16              

Files Changed	Coverage Δ
R/H2.R	91.66% <100.00%> (+2.77%)	⬆️
R/H2_overall.R	93.75% <100.00%> (+0.41%)	⬆️
R/H2_pairwise.R	95.45% <100.00%> (-0.20%)	⬇️
R/H2_threeway.R	95.83% <100.00%> (-0.17%)	⬇️
R/hstats.R	100.00% <100.00%> (ø)

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