MessageBodyStream is too naive

[sliekens]

Currently, the MessageBodyStream class will always use the value of the Content-Length header as the stream length. However, some responses specify a Content-Length header that is strictly informational.

https://github.com/StevenLiekens/http-client/blob/27380538dff195be187e5f52e43354b63760a508/src/Http/MessageBodyStream.cs

The following response types may have a Content-Length but no message body:

• Any response that is the result of a HEAD request
• Any response with status code 1xx, 204 or 304

[sliekens]

Additionally, chunked responses use an entirely different mechanism. Consider adding a separate ChunkedMessageBodyStream class for that use-case.