bpo-41002: Optimize HTTPResponse.read with a given amount (GH-20943)

bpo-41002: Optimize HTTPResponse.read with a given amount (GH-20943)

I've done the implementation for both non-chunked and chunked reads. I haven't benchmarked chunked reads because I don't currently have a convenient way to generate a high-bandwidth chunked stream, but I don't see any reason that it shouldn't enjoy the same benefits that the non-chunked case does. I've used the benchmark attached to the bpo bug to verify that performance now matches the unsized read case.

Automerge-Triggered-By: @methane