forbid use of bare LF as chunk header terminator

[kazuho]

As discussed in #60, RFC 9112 mandates use of CRLF (i.e., forbids use of bare LF) at the end of chunk headers.

This pull request enforces that.

At the same time it continues to accept bare LF inside trailers, as it is a list of fields and RFC 9112 allows parsers to accept bare LFs at the end of each field. This behavior might not be necessary, but it retains consistency with phr_parse_headers which is the function that is used for parsing trailers (note: it is only when consume_trailer bit is set that the trailers are consumed by phr_decode_chunked; if the flag is not, it is the responsibility of the application to parse the trailers using phr_parse_headers).