replace requests with httpx and factor out clients (#1574)
* input downloads, output uploads, and webhooks are now handled by ClientManager, which persists for the lifetime of runner, allowing us to reuse connections, which may significantly help with large uploads.
* although I was originally going to drop output_file_prefix, it's not actually hard to maintain. the behavior is changed now and objects are uploaded as soon as they're outputted rather than after the prediction is completed.
* there's an ugly hack with uploading an empty body to get the redirect instead of making api time out from trying to upload an 140GB file. that can be fixed by implemented an MPU endpoint and/or a "fetch upload url" endpoint.
* the behavior of the non-indempotent endpoint is changed; the id is now randomly generated if it's not provided in the body. this isn't strictly required for this change alone, but is hard to carve out.
* the behavior of Path is changed significantly. see https://www.notion.so/replicate/Cog-Setup-Path-Problem-2fc41d40bcaf47579ccd8b2f4c71ee24
Signed-off-by: technillogue <technillogue@gmail.com>
Co-authored-by: Mattt <mattt@replicate.com>
