Mypy is failing while checking finetune_eval.py

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As long as there is duplicated naming of finetune_eval in `benchmarks/imagenet/resnet50/finetune_eval.py` and `benchmarks/imagenet/vitb16/finetune_eval.py` mypy throws an exception when running `pre-commit run --all-files`:

```plaintext
benchmarks/imagenet/vitb16/finetune_eval.py: error: Duplicate module named "finetune_eval" (also at "benchmarks/imagenet/resnet50/finetune_eval.py")
benchmarks/imagenet/vitb16/finetune_eval.py: note: See https://mypy.readthedocs.io/en/stable/running_mypy.html#mapping-file-paths-to-modules for more info
benchmarks/imagenet/vitb16/finetune_eval.py: note: Common resolutions include: a) using `--exclude` to avoid checking one of them, b) adding `__init__.py` somewhere, c) using `--explicit-package-bases` or adjusting MYPYPATH
Found 1 error in 1 file (errors prevented further checking)
```

There are 3 solutions:
- Change the namings;
- Add __init__.py to form packages;
- Add the workaround to contributing manual.

Start with benchmarks/imagenet/resnet50/finetune_eval.py and benchmarks/imagenet/vitb16/finetune_eval.py, then run `pre-commit run --all-files` to reproduce the duplicate-module error. Review the three resolutions listed in the issue and the contributing manual before choosing one. Done means the duplicate mypy error is resolved and the pre-commit check completes successfully.

Written by the indexing model from the issue text.