Add IMO Bench dataset validation script and documentation

[yash27-lab]

This PR adds a validation script for the IMO Bench datasets.

Changes:

• Added imobench/validate_imobench.py to validate schema and integrity of CSV files.
• Updated imobench/README.md with instructions on how to run the validation script.

The validation script checks:

• Required columns
• Basic schema consistency
• File readability and formatting

This improves dataset robustness and helps prevent malformed submissions or accidental schema regressions.

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.