refactor (Big Number): Clean up data fetching

[ericpgreen2]

This PR:

• Pulls the big number API requests out of the timeseries-data-store and into a dedicated big-number-queries.ts file
• Uses stable Query Observers (made possible via TanStack Query v5)

Checklist:

• [ ] Covered by tests
• [ ] Ran it and it works as intended
• [ ] Reviewed the diff before requesting a review
• [ ] Checked for unhandled edge cases
• [ ] Linked the issues it closes
• [ ] Checked if the docs need to be updated
• [ ] Intend to cherry-pick into the release branch
• [ ] I'm proud of this work!