Add warm_start

[mirand863]

• Add tests to verify that the example in the documentation is correct
• Implement code

Closes #70

[codecov]

Codecov Report

Merging #73 (0dfa620) into main (8ec3e50) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main      #73   +/-   ##
=======================================
  Coverage   98.33%   98.33%           
=======================================
  Files           8        8           
  Lines         541      542    +1     
=======================================
+ Hits          532      533    +1     
  Misses          9        9           

Impacted Files	Coverage Δ
hiclass/LocalClassifierPerNode.py	100.00% <ø> (ø)
hiclass/LocalClassifierPerParentNode.py	100.00% <ø> (ø)
hiclass/HierarchicalClassifier.py	95.45% <100.00%> (+0.02%)	⬆️

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