Add multinomial regression model

[ismailsenoz]

This PR adds multinomial regression model to RxInferServer. The model is merely a copy of what we have in RxInferExamples.

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[github-actions]

🤖 Code Formatting

Your PR still has some code formatting issues. I've updated PR #103 with the necessary formatting changes.

You can merge that PR into this branch to fix the code style check.

Alternatively, you can run make format locally and push the changes yourself.