Add interleaving for multi-source retrieval

[ystoneman]

Enable interleaving from multiple sources so chatbot scales and synthesizes as connectors increase. Suboptimal aggregation causes relevance and length issues as sources grow.

Interleaving strategy:

• Chunk into 100-400 word segments
• Re-rank chunks per source
• Interleave top chunks
• Pass to LLM prompt

Benefits:

• Scales to more sources
• Produces relevant, synthesized responses
• Avoids length limits

Got this idea from the "Interleaving" section of Cohere's guide on RAG for large-scale data, which includes this diagram: