Add HartleyRao for `SurveyDesign`

[smishr]

• Add back HartleyRao function for variance estimation
• Integrate with total with SurveyDesign
• Add tests

I couldnt get R to match these results like for like. R isnt quite using Hartley Rao algorithm.

[codecov-commenter]

Codecov Report

Merging #227 (2a90d8a) into main (f5d256b) will not change coverage. The diff coverage is 100.00%.

@@            Coverage Diff            @@
##              main      #227   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           12        13    +1     
  Lines          183       188    +5     
=========================================
+ Hits           183       188    +5     

Impacted Files	Coverage Δ
src/hr.jl	100.00% <100.00%> (ø)
src/total.jl	100.00% <100.00%> (ø)

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[smishr]

moved to #247