MEDIUM: h1-htx: Add a function to parse contiguous small chunks

MEDIUM: h1-htx: Add a function to parse contiguous small chunks

Add h1_parse_full_contig_chunks() function to parse full contiguous chunks.
This function neither handles incomplete chunks nor wrapping buffers. It is
designed to efficiently parse a buffer with several small chunks. Of course,
there is no zero copy here because it is not possible. This function is a
bit tricky and all changes may a have a impact. This one may probably be
optimized, but it is good enough for now and not too complex.

The main function (h1_parse_msg_chunks) always tries to use this function
when the HTTP parser is waiting for a chunk size. In this case, there is no
zero-copy, so there is no reason to call the generic version to parse the
chunk. However, if some unparsed data remain after this step, the generic
function is called. This way, wrapping data and incomplete chunks may be
parsed.

Quick tests show it is now slightly faster in all cases than the legacy
mode.