Chaitanya Giri

#### Description of Change Implemented inorder tree traversal #### Checklist - [x] Added description of change - [x] Added file name matches [File name guidelines](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/CONTRIBUTING.md#New-File-Name-guidelines) - [x] Added tests and...

### Feature description There are many commonly used machine learning models already present but there is no implementation of the xgboost model present. Implement: 1) XGBClassifier - for classification tasks...