Add CODEBASE_REVIEW_TASKS.md with targeted fix and test tasks

[yeze5421]

Motivation

• The repository currently contains a single script mlip.py and no automated tests, so a small, actionable task list was added to surface prioritized fixes (typo, bug, docs) and a minimal test plan.

Description

• Add CODEBASE_REVIEW_TASKS.md which lists four concise tasks: a typo fix to change the section comment # Physics: Lennard-Jones toy label, a bug-hardening task to make split_dataset() robust against empty validation splits, a documentation/comment clarification for the inverse-distance descriptor, and a proposal for a minimal pytest suite covering core invariants.

Testing

• No automated unit tests exist in the repository, so no automated tests were run for this change.

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Codex Task