n+1 and memory bloat in page rendering

[thibaudcolas]

The site is regularly going well over its memory quota in production, and generally has poor performance. This is very detrimental for users. And I think there are easy pickings on page rendering specifically. and llms.txt generation.

Solutions that I think we should try:

• Set up assertions on query count in tests
• Reduce overfetching / fetch better just by reworking the code
• Caching with invalidation on revision IDs