Fix streaming response compression

[kyri-petrou]

This PR fixes a bug where if a streaming response has a known size, netty fails to compress it and the response is all botched up. The main culprit is that the ByteBuf objects need to be wrapped in a DefaultHttpResponse prior to writing them to the Netty channel for Netty to be able to compress them properly.

In addition, there is also another minor bug where the content-length from headers is not being extracted correctly, as it seems that netty will mutate the response object after writeAndFlush has been invoked on it, which means we need to extract the content-length before we call it

To reproduce, run the following code and open http://localhost:8080/foo on a browser:

import zio.*
import zio.http.*
import zio.http.Server.Config.ResponseCompressionConfig
import zio.stream.ZStream

object Foo extends ZIOAppDefault {
  val body = Chunk.fromArray("hello world".getBytes)

  val foo =
    Method.GET / "foo" -> handler(
      ZIO.succeed(Response(body = Body.fromStream(ZStream.fromChunk(body), body.length)))
    )

  override val run =
    Server
      .serve(Routes(foo).toHttpApp)
      .provide(
        Server.live,
        ZLayer.succeed(Server.Config.default.port(8080).responseCompression(ResponseCompressionConfig.default)),
      )
}