Added NumberOfLeaves to FastForestRegression and FastForestOva options

[JoshuaSloan]

Fixes #7498

The NumberOfLeaves hyperparameter was not updating in FastForest AutoML experiments for regression and multiclass classification tasks (see regression example in the associated issue, which was trained on the California Housing dataset and optimizing for root mean squared error).

Consequently, the trial parameters reported via an experiment monitor's final ReportBestTrial() method were not aligning with the actual model produced by the experiment. Additionally, model performance was hurt due to the static hyperparameter constraint.

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[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 69.00%. Comparing base (fb39755) to head (b232462).

Files with missing lines	Patch %	Lines
...AutoML/SweepableEstimator/Estimators/FastForest.cs	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7499      +/-   ##
==========================================
- Coverage   69.01%   69.00%   -0.01%     
==========================================
  Files        1482     1482              
  Lines      273999   274001       +2     
  Branches    28258    28258              
==========================================
- Hits       189093   189083      -10     
- Misses      77520    77533      +13     
+ Partials     7386     7385       -1     

Flag	Coverage Δ
Debug	69.00% <50.00%> (-0.01%)	⬇️
production	63.30% <50.00%> (-0.01%)	⬇️
test	89.45% <ø> (-0.01%)	⬇️

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Files with missing lines	Coverage Δ
...AutoML/SweepableEstimator/Estimators/FastForest.cs	33.33% <50.00%> (-34.24%)	⬇️

... and 6 files with indirect coverage changes

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