[store] Adopt useSyncExternalStore for @slimlib/store

[kshutkin]

To prevent tearing adopt useSyncExternalStore for @slimlib/store. Take a look how it works with other stores and how and if it is possible with fully mutable approach.

[kshutkin]

Check tests in https://github.com/dai-shi/will-this-react-global-state-work-in-concurrent-rendering/

[kshutkin]

Looks like React comparing snapshots using Object.is. In my implementation if callback is called than store is changed and because it is always the same underlying object Object.is is always true and React never re-renders component. If I try to deep clone or just clone object on each getSnapshot it does not work either as React re-rendering component in infinite loop. So next solution will be to only clone after callback called. This means that to support useSyncExternalStore we need a lot of additional logic and memory allocation so probably it needs more experimentation/performance testing.

[kshutkin]

After some experiments I'm not convinced that supporting useSyncExternalStore helps with tearing with this specific store implementation. I've tried solution from my previous comment and it works but according to tests https://github.com/dai-shi/will-this-react-global-state-work-in-concurrent-rendering/ I still have the same cases failed. More or less it is probably because despite the fact that we have sync getSnapshot the store itself is not sync but works through microtask. Generally it helps to defer update to less busy time when microtask resolved but it hurts if we want more granular timeslicing. So far it should be closed as Won't fix but can be reconsidered later if better approach proposed.