Feature Request: Support Http trailers in chunked transfer

Trailers in chunked transfer are described by rfc3230-section 4.1. Net/http does not support setting trailers nor is there a way for users to implement chunked trailers on top of net/http. The grammar is (combining section 4.1 and 4.1.2):

chunked-body   = *chunk
                      last-chunk
                      trailer-part
                      CRLF

     chunk          = chunk-size [ chunk-ext ] CRLF
                      chunk-data CRLF
     chunk-size     = 1*HEXDIG
     last-chunk     = 1*("0") [ chunk-ext ] CRLF

     chunk-data     = 1*OCTET ; a sequence of chunk-size octets
     trailer-part   = *( header-field CRLF )

When a body_stream is set and the transfer-encoding is chunked, GenericRequest#send_request_with_body_stream creates a Chunker . The Chunker correctly follows the rfc in writing out the chunks and writing the last-chunk as "0\r\n\r\n". However, there are no hooks or support for writing the trailer-part.

Read RFC 7230 section 4.1, then inspect lib/net/http/generic_request.rb, especially Chunker and GenericRequest#send_request_with_body_stream. Define how callers provide trailers and verify that chunked bodies emit the trailer-part after the last-chunk and final CRLF.