(read-http-response channel) -> <http-response>
Given a channel, read from it and create an <http-response> object.
>> (define resp (make-channel))
:: [channel 580450]
>> (write-http-response resp 200 "Peachy" '("Content-Type: text/text")
"Life is peachy")
:: null
>> (read-http-response resp)
:: [http-response [vector null 200 "Peachy" [dict ...] "Life is peachy" #f
[primitive input]]]