Add CNN class for handling MNIST dataset

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Description

This PR adds a new CNN class in the cnn.py file to handle the MNIST dataset. The CNN class is imported into main.py to define the model for training on the MNIST dataset.

Summary of Changes

• Created a new file src/cnn.py to contain the CNN class.
• Imported necessary modules in cnn.py for defining the CNN architecture.
• Defined the CNN class with the required layers and methods.
• Added docstrings and comments to the CNN class for clarity.
• Modified src/main.py to import the CNN class from cnn.py.
• Instantiated the CNN class to define the model for training on the MNIST dataset.
• Added comments to explain the new code.

Please review and merge this PR. Thank you!

Fixes #9.

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Rollback Files For Sweep

• Rollback changes to src/main.py
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