add diatomic download and share utilities from phonons download

[joehart2001]

Pre-review checklist for PR author

PR author must check the checkboxes below when creating the PR.

• I've confirmed the contribution guidelines.
• I have reviewed and understand all AI-generated code in this PR.
• I have added human-written tests for the new logic.
• I have properly cited any upstream algorithms or libraries the AI utilized.
• I have disclosed significant AI tool usage in the PR description.

Summary

Linked issue

Resolves #

Testing

[joehart2001]

@ElliottKasoar it keeps refusing my changes to pass the pre-commit, any idea?

[ElliottKasoar]

Is this supposed to be labeled as new model?

The functions you're importing don't seem to exist? It's an odd manifestation, but probably why.

[joehart2001]

Is this supposed to be labeled as new model?

The functions you're importing don't seem to exist? It's an odd manifestation, but probably why.

sorry nope. ahh i had forgot to add a new utils file, all good now