Improve lesson generation with chain of density for summarization and other Q&A techniques

Related to #10

- Chain of Density
- https://www.reddit.com/r/LangChain/comments/16mv84c/from_sparse_to_dense_gpt4_summarization_with/
- https://github.com/richawo/chain-of-density

Start by reading related issue #10 and the linked Chain of Density discussion and repository. The issue names no files, tests, or entry points, so first identify where lesson generation and the other Q&A techniques are implemented. Done should be demonstrated by a defined, tested improvement to lesson generation using the requested summarization approach.

Written by the indexing model from the issue text.