Add new line token in tokenizer

[boat1603]

Why this PR

Why we need this PR?
This PR is about add \n token in the tokenizer trainer.

Changes

• Write some changes here

Related Issues

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Checklist

• PR should be in the Naming convention
• Assign yourself in to Assigneees
• Tag related issues
• Constants name should be ALL_CAPITAL, function name should be snake_case, and class name should be CamelCase
• complex function/algorithm should have Docstring
• 1 PR should not have more than 200 lines changes (Exception for test files). If more than that please open multiple PRs
• At least PR reviewer must come from the task's team (model, eval, data)