feat: add support for concurrent mode

[boschni]

This PR adds support for concurrent mode rendering.

Render functions will now only have these side effects:

• Creating a cache entry (should be allowed)
• Dispatching a GET request (should be allowed)

When calling a render function, it will return an optimistic result, without actually changing the observer state. The observer state will only be changed when new options are set/committed in an effect.

Unfortunately I was not able to keep the referential integrity of the result object between renders because we do not know which optimistic result will eventually get committed.

Fixes #1536

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[tannerlinsley]

🎉 This PR is included in version 3.9.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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[klarstrup]

I don't have a minimal repro at present, but I believe this change has broken useInfiniteQuery SSR in my app. Worked on 3.8.3, simply renders with data: undefined on 3.9.0.

[boschni]

Could you provide some more information? Does it only apply to infinite queries? What options are you using? Is your usage similar to https://github.com/tannerlinsley/react-query/tree/master/examples/nextjs ?

[klarstrup]

My specific setup is using react-ssr-prepass but that example is similar enough I believe. I'm working on a minimal repro.