NGINX structural enhancements for HTTP/2 performance

This post details structural enhancements made to NGINX to improve HTTP/2 performance, specifically to increase the 'Potential' for prioritization algorithms. Key changes include: 1. HTTP/2 frame write queue reclamation: allowing unwritten frames from a partial write to be restored to per-stream queues for re-prioritization, rather than being held until the backlog clears. 2. HTTP/2 frame write event re-ordering: modifying the NGINX workflow to process frames from multiple upstream connections into per-stream queues before a single prioritization and write event, enabling frames from different streams to be in closer proximity for prioritization.