POPPY-0031: Parse trailer in http chunked requests

Chunked transfer encoding is a streaming data transfer mechanism available in version 1.1 of the Hypertext Transfer Protocol (HTTP). In chunked transfer encoding, the data stream is divided into a series of non-overlapping "chunks". The chunks are sent out and received independently of one another.

Chunked encoding allows the sender to send additional header fields after the message body. This is important in cases where values of a field cannot be known until the content has been produced, such as when the content of the message must be digitally signed. Without chunked encoding, the sender would have to buffer the content until it was complete in order to calculate a field value and send it before the content.

We should be able to parse those trailers.

The issue names no files, tests, or entry point. Begin by locating the HTTP/1.1 chunked-request parsing code and its existing tests, then define expected trailer handling from the protocol description. Done means trailers are parsed and covered by tests.

Written by the indexing model from the issue text.