Port over changes from prog_algs hotfix v1.5.1

[teubert]

Ports over a few bugfix to the Monte Carlo. Fixes issue where horizon is not applied correctly.

Also changed the example to use MultivariateNormal Distribution and added associated tests.

Thank you @kjjarvis for your work on this.

[github-actions]

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• Ensure that each PR adding a new feature should include a test verifying that feature.
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[codecov-commenter]

Codecov Report

Merging #75 (72716fd) into dev (81d8448) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##              dev      #75   +/-   ##
=======================================
  Coverage   84.25%   84.26%           
=======================================
  Files          99       99           
  Lines       10164    10167    +3     
=======================================
+ Hits         8564     8567    +3     
  Misses       1600     1600           

Files Changed	Coverage Δ
src/progpy/predictors/monte_carlo.py	91.91% <100.00%> (+0.25%)	⬆️

[kjjarvis]

Port over changes look good