Add support for MultivariateStats

[tpoisot]

Cf. #203

[github-actions]

Documentation for this PR at https://poisotlab.github.io/SpeciesDistributionToolkit.jl/previews/PR204/

[gottacatchenall]

This could be something to work off of, but there never was a convenient solution to both StatsBase and MVStats both exporting fit and transform

[codecov-commenter]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (a46e8db) 52.92% compared to head (b4ce53e) 47.05%.

❗ Current head b4ce53e differs from pull request most recent head 5a554b9. Consider uploading reports for the commit 5a554b9 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #204      +/-   ##
==========================================
- Coverage   52.92%   47.05%   -5.87%     
==========================================
  Files          59       47      -12     
  Lines        1708     1394     -314     
==========================================
- Hits          904      656     -248     
+ Misses        804      738      -66     

Flag	Coverage Δ
unittests	47.05% <ø> (-5.87%)	⬇️

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see 12 files with indirect coverage changes

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