Correctly handle jobs that can have multiple responses

[ported-pw]

Some jobs can have multiple responses (such as CMsgClientPICSProductInfoResponse with its response_pending field). This commit handles this. I am not entirely happy with the code as it somewhat breaks the barrier between what Filter and ConnectionTrait are supposed to handle, but I'm not sure a better solution exists within the current architecture.

The result/error type is also up for debate - we should probably return partially anyway even if there was an error, and let the user decide if they want it or not. Maybe we also want to return a broadcast::Receiver instead?

As a reference, see for example: https://github.com/SteamRE/SteamKit/blob/b4e4cb929b55c45bf262ab2b293be2424f81975a/SteamKit2/SteamKit2/Steam/Handlers/SteamApps/SteamApps.cs#L178

I guess this could be expanded to collect the data into a reasonable structure, but this would seem more suited to a high-level wrapper:
https://github.com/SteamRE/SteamKit/blob/master/SteamKit2/SteamKit2/Steam/Handlers/SteamApps/Callbacks.cs#L629

[icewind1991]

I wonder if we can have jobs marked with JobMultiple return the Vec from the regular job method instead of requiring a separate one. Maybe with some associated type magic.

[icewind1991]

I wonder if we can have jobs marked with JobMultiple return the Vec from the regular job method instead of requiring a separate one. Maybe with some associated type magic.

Couldn't figure out anything that wouldn't hurt ergonomics so lets just do it like this for now

[icewind1991]

I did change the job_multi function to return a Stream instead of a Vec