[llm unify 7/n] Summarize

[HenryL27]

Again, general lack of confidence in this.

Turns summarize document from an iterative folding strategy to a heirarchical strategy.
Uses math + jinja to generate a summary every k elements for the next k elements (and then repeat with k^2 and a stride of k, etc until k^n > n_elements).

Integrates into summarize_data by slightly changing how that reduce happens. Had to make a separate (similar) prompt for that. Should probably factor most of the jinja logic out as fragments.

I probably broke something in luna but all the unittests passed so idk.

Also not sure about some of the names.