[Improvement]: Ensure Models Consistency

[azooz2003-bit]

Description

A lot of the models are poorly written and/or lack certain properties. e.g. for fixed String properties, we should use an enum. Structs for some properties. Some properties don't need to be optional - compare with Official Canvas iOS attached below.

Relevant Resources

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• Canvas iOS Official: https://github.com/instructure/canvas-ios/blob/master/Core/Core/Courses/APICourse.swift

Child Issues

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Implementation Plan (optional)

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