Fix slow MP4 playback via proxy (switch to net/http streaming + range handling)

[Pal-droid]

Summary

This PR fixes very slow playback for certain proxied MP4 streams by changing the proxy’s upstream HTTP behavior and response semantics to better match what browsers/video players expect.

Changes

• Use net/http client + custom transport for upstream requests:

  • ForceAttemptHTTP2: false
  • DisableCompression: true
  • Accept-Encoding: identity
  • long timeout for streaming

• Strip RFC7230 hop-by-hop headers when proxying upstream headers.

• For non-HLS responses:

  • send minimal MP4-friendly headers (Content-Type, Accept-Ranges, Content-Range, Content-Length when safe)
  • return 206 Partial Content when the client sends Range
  • stream response body with periodic flush and context cancellation handling.

• Preserve upstream status code for HLS playlist responses.

[5rahim]

thanks for the PR, but i think this is trying to fix an issue buy doing too much at once, it should be scoped to the issue at hand first (which is the non-HLS path).
i'd suggest testing things step by step, e.g. as i see it, the likely culprit can be: the timeout length from the req client, compression or hopbyhop header or all three combined. if that doesn't do it you can then conditionally keep the content-length header like you're doing. if that still doesn't do it you could first, try to overwrite the content-type, then replace c.Stream and so on.

that way in the end, we know what the root cause is for future reference.

[Pal-droid]

I tested the changes step-by-step (timeout, identity/no compression, hop-by-hop headers, conditional Content-Length, and replacing c.Stream). The only change that consistently fixed it was switching the non-HLS upstream fetch from req/v3 to net/http (with HTTP/2 off + identity/no compression).

[5rahim]

i investigated further since you said that req/v3 was the bottleneck and indeed simply adding DisableAutoReadResponse() fixed it because it was buffering the vid until timeout.

[5rahim]

i can still merge it as a contribution but you'll have to revert everything and add DisableAutoReadResponse(). after req.C()., the other changes aren't necessary

[Pal-droid]

made those changes and noticed playback was fine but seeking was kinda slow