added doc for Trainer.scala

[bashirk]

Description

This PR adds inline documentation to the scala_core/src/main/scala/org/nimbleedge/envisedge/Trainer.scala file.

Relevant Issue

Checklist

• [x] I have followed the Contribution Guidelines and Code of Conduct
• [x] I have commented my code following the NimbleEdge Styleguide

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[divyanshugit]

@bashirk Content-wise, it's looking good. But it needs a few modifications like:

• In scala, we write the inline comments before the functions, method, or class. So, please follow it.

Thanks