Ensure query is only used once per query, rather than per source

[will-langdale]

This is a draft PR to show some highly AI-authored code for ensuring only one call is made to query().

Warning

This draft PR that mainly exists to retain the high-level changes that fix the problem. It's extremely noisy and messy, and I haven't had time to cook it down to the important bits.

🛠️ Changes proposed in this pull request

• Update the query() SQL query to return the right data
• Extend the query data Arrow schema to include a dictionary of the various sources
• Update the client to receive and process the new data

👀 Guidance to review

None.

🤖 AI declaration

All of it, none of it reviewed.

🔗 Relevant links

None.

✅ Checklist:

• This is the smallest, simplest solution to the problem
• I've read our code standards and this code follows them
• All new code is tested
• I've updated all relevant documentation (select all that apply)
  • API documentation (docstrings and indexes)
  • Tutorials
  • Developer docs