feat: add remote function query.stream

[dummdidumm]

• streams are deduplicated on the client, i.e. same resource+payload == same stream instance
• a stream is kept open as long as it's either in a reactive context or someone iterates over it. Streams can close when noone listens anymore and open back up when someone does again
• cannot iterate on the server right now, only retrieve the first value via promise
• cannot refresh/override (doesn't make sense)

WIP, builds on top of the query-batch PR to avoid merge conflicts like crazy since they touch the same files; the batch PR should be merged first

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[Rich-Harris]

How confident are we about the deduplication part? For cases where you're streaming a live view of some database query, that makes sense, but are there cases more like this?

for await (const n of countToTen()) {
  console.log(n);
}

It would be weird if I did that and it started at 7 because of something happening in an unrelated component. Genuinely not sure what the right way to think about this is.

[dummdidumm]

yeah I had the same thought already. Hard to tell, both ways make sense - which maybe means we need to give people some way to tell what it is?

Update: maybe it should be "each invocation is a separate stream". Then you can still deduplicate yourself if you want to.