use buffer on response in clientDoDeadline

[brian-armstrong-discord]

we want to do this so that we can reuse the response's existing buffer rather than allocating new ones. allocating memory is expensive

[night]

isn't it doing that by default? the code as written prior seems to swap the body to reset it after an error occurs.. otherwise it is using the same

Edit: also worth noting that it shouldn't really be allocating unless it needs to.. it's pooling old buffers in http.go for reuse

[brian-armstrong-discord]

the key change is L921. L941 is just necessary in order to swap back.

not sure if this actually works - i havent quite got it to do the right thing in media proxy yet. but it does actually use my buffer now, whereas it didnt previously.

[brian-armstrong-discord]

also for clarity, in media proxy, fasthttp does not own the buffers, a different part of the server does. so we are in a bad situation because we fasthttp creates a ton of garbage and we have to copy out of its buffers. the idea here is to make fasthttp stop allocating entirely.