Add CNN class for MNIST and update main.py and api.py (✓ Sandbox Passed)

[sweep-nightly[bot]]

Description

This pull request adds a new CNN class for MNIST and updates the main.py and api.py files.

Summary

• Added CNN class in cnn.py
• Updated imports in api.py
• Updated model instantiation in api.py
• Updated transform in api.py
• Updated model instantiation in main.py
• Updated transform in main.py
• Updated model training in main.py
• Updated model saving in main.py

Fixes #9.

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[sweep-nightly[bot]]

Sandbox Executions

• [X] Ran sandbox for src/cnn.py. ✓

  Sandbox logs for

trunk fmt src/cnn.py || exit 0 1/2 ✓

Checked 1 file
✔ No issues
Run trunk upgrade to upgrade 1 linter

trunk check --fix --filter=-ruff --print-failures src/cnn.py 2/2 ✓

Checked 1 file
✔ No issues

• [X] Ran sandbox for src/main.py. ✓

  Sandbox logs for https://github.com/sweepai/evals/commit/d09aad01aca21d5da2fecbdc78cff73210bcf583

trunk fmt src/main.py || exit 0 1/2 ✓

 ✔ Formatted src/main.py
Re-checking autofixed files...

 ✔ Formatted src/main.py
Re-checking autofixed files...

Checked 1 file
✔ No issues
Run trunk upgrade to upgrade 1 linter

trunk check --fix --filter=-ruff --print-failures src/main.py 2/2 ✓

Checked 1 file
✔ No issues

• [X] Ran sandbox for src/api.py. ✓

  Sandbox logs for https://github.com/sweepai/evals/commit/0c26d09787bade42df5a248bf6b73dd74ea8ccf7

trunk fmt src/api.py || exit 0 1/2 ✓

 ✔ Formatted src/api.py
Re-checking autofixed files...

 ✔ Formatted src/api.py
Re-checking autofixed files...

Checked 1 file
✔ No issues
Run trunk upgrade to upgrade 1 linter

trunk check --fix --filter=-ruff --print-failures src/api.py 2/2 ✓

Checked 1 file
✔ No issues

[sweep-nightly[bot]]

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• [ ] Apply: All docstrings and comments should be up to date.
• [ ] Apply: Code should be properly formatted and indented.
• [ ] Apply: Variable and function names should be descriptive and follow a consistent naming convention.
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• [ ] Apply: There should be no unused imports or variables.
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