Extensions to Compress and Derive Fields in HTTP Datagrams

This document defines extensions for HTTP Datagram-based protocols that improve transmission efficiency by introducing templates for compressing or deriving datagram fields. These templates allow endpoints to define parts of datagrams that are static and can be removed, and other parts that can be derived (such as packet lengths and checksum values). Additionally, this document defines a checksum offload procedure enabling receivers to complete Internet checksums using sender- provided partial values. These optimisations reduce per-packet overhead, processing cost, and increase the effective maximum transmission unit (MTU) when datagrams are encapsulated in QUIC DATAGRAM frames.