Make Reader unusable after io.EOF and Writer unusable after Close

[nhooyr]

I originally did not do this because I didn't want them to hold state so they could be stored as a value inside the interface{} but that isn't possible, Go is allocating it on the heap for me as interface{} can only contain a pointer.

[nhooyr]

Something else I want to do is to remove the read and write loop goroutines. The goroutine that wants to write/read should hold the lock itself.

[nhooyr]

Ok I got it, we still need another goroutine to close the connection. What we should do is have the extra loop goroutines cancel the connection instead of the calling goroutine. Would simplify code big time.