Fix Metrics in XGBoostClassifier and XGBoostRegressor

[amirhessam88]

Description

• Removed metrics from XGBoostClassifier and XGBoostRegressor since there is no need to have it. metrics is being used in _cv() module only and eval_metrics still can be used as a params item.
• Updated unit-tests accoringly.
• Update example notebooks.

TODO

• [FEATURE]: Expose all XGBoost Metrics in XGBoost Classifier, Regressor, and Feature Selector #146
  Resolves: #issue-number-here

Pull Request Checklist

• Added tests for added or changed code.
• Added documentation for changed code.

[codecov]

Codecov Report

Base: 67.53% // Head: 67.50% // Decreases project coverage by -0.03% ⚠️

Coverage data is based on head (09662e5) compared to base (e16e609).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #147      +/-   ##
==========================================
- Coverage   67.53%   67.50%   -0.04%     
==========================================
  Files          22       22              
  Lines        1999     1997       -2     
  Branches      302      302              
==========================================
- Hits         1350     1348       -2     
  Misses        602      602              
  Partials       47       47              

Flag	Coverage Δ
unittests	67.50% <100.00%> (-0.04%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/slickml/classification/_xgboost.py	100.00% <ø> (ø)
src/slickml/regression/_xgboost.py	100.00% <ø> (ø)
src/slickml/classification/_xgboostcv.py	100.00% <100.00%> (ø)
src/slickml/regression/_xgboostcv.py	100.00% <100.00%> (ø)

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