Show DC stats in tooltips for RIG

[hqpho]

For RIG answers:

• Don't show inline DC stats. Instead show DC stat with label in a tooltip when an LLM stat is hovered over.
• When an LLM stat in SxS UI doesn't have an associated DC stat, don't highlight it or show a tooltip. (For regular eval UI, still highlight but don't add a tooltip.)

Other changes:

• Change "Why?" free-text form field label to "Comments (optional)"
• Show "Loading answer..." when fetching answers, so answers are never out of sync with the feedback form.
• Fetch all call data when initially loading each spreadsheet
• Don't limit some sheet calls by column (fetch more data including possibly extraneous data in exchange for making fewer fetches)
• Minor naming updates for readability

Screencast

[hqpho]

nice, code looks good, but can we try out the tooltip content changes we talked about in the chat?

yep, I'm working on them; they're non-trivial since the detailed call info isn't in DocInfo. Thanks for the preliminary review!