Closing a stream can throw if messages aren't waited for

[glbrntt]

If a client response handler returns before all messages have been received (i.e. the user has what they need from the response) then the stream might throw because of an unclean close.

This can happens because the HTTP/2 stream closes uncleanly and NIO's async channel throws this error.

[gjcairo]

This has been resolved in apple/swift-nio#3032 and the fix is present in NIO since 2.78.0, which this package already depends on. The workaround is removed in #63. Closing.