Refactor training loop from script to class

[sweep-nightly]

Description

This PR refactors the training loop from a script to a class in order to improve code modularity and maintainability. The training loop is encapsulated in a new class called Trainer in the main.py file. The Trainer class has methods for training a single epoch, evaluating the model, and running the entire training process. The api.py file is also updated to import the Trainer class instead of the Net class.

Summary of Changes

• Created a new class Trainer in main.py to encapsulate the training loop.
• Added attributes model, optimizer, criterion, and dataloader to the Trainer class.
• Implemented the train_epoch method in the Trainer class to perform training for a single epoch.
• Implemented the evaluate method in the Trainer class to evaluate the model on the training data.
• Implemented the train method in the Trainer class to run the entire training process.
• Updated the import statement in api.py to import the Trainer class instead of the Net class.
• Updated the code in api.py to create an instance of the Trainer class and access its model attribute.

Please review and merge this PR. Thank you!

Fixes #6.

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Rollback Files For Sweep

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

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