Add CNN class for MNIST handling and import it to main.py

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Description

This PR adds a new CNN class for handling the MNIST dataset and imports it into the main.py file. The existing implementation in main.py uses a simple feed-forward neural network, and this PR replaces it with the new CNN class.

Summary of Changes

• Created a new file src/cnn.py to define the CNN class.
• Implemented the CNN class using PyTorch, with appropriate layers for handling 28x28 grayscale images.
• Updated the import statement in src/main.py to import the CNN class from cnn.py.
• Replaced the instantiation of the existing Net class with the new CNN class in the "Define the PyTorch Model" section of src/main.py.
• Updated the training loop in src/main.py to accommodate the changes in the network architecture.
• Added docstrings and comments to the CNN class and its methods, following the project's conventions.

Please review the changes and merge this PR if it meets the requirements.

Fixes #9.

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Rollback Files For Sweep

• Rollback changes to src/cnn.py
• Rollback changes to src/main.py
• Rollback changes to src/main.py
• Rollback changes to src/main.py
• Rollback changes to src/main.py

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[wwzeng1]

src/api.py:5:0: E0611: No name 'Net' in module 'main'

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🚀 Wrote Changes

Done.