Todos for upcoming Go releases

[akshayjshah]

This issue tracks small cleanups we should do as we drop support for old Go releases.

Go 1.18

• Remove the asMaxBytesError function that uses string comparisons.

Go 1.19

• Check for HTTP/2 error codes using x/net/http2.StreamError and errors.As (though we'll need to discuss whether we want an x/net dependency)
• Explore the new http.ResponseController's capabilities and how we might expose them. In particular, read and write deadlines would be nice! (see Go 1.21 below)

Go 1.20

• Use http.ResponseController.EnableFullDuplex to allow bidi streaming over HTTP/1.1.

Go 1.21

• Explore the use of read and write deadlines on http.ResponseController (now that panic bug is fixed in Go 1.22). Also see Options for safely handling slow clients #604.