fix: update flushSync for new reconciler

[krispya]

Here begins my introduction to triaging the React reconciler. In this PR you will see...

• react-reconciler updated to 0.32 along with the types.
• Removed type shimming that was fixed by the new type package. Note: The reconciler types still aren't quite correct but that is another project.
• flushSync is now properly using the internal flushSyncFromReconciler which mimics the flushSync behavior from react-dom: https://github.com/facebook/react/blob/main/packages/react-dom/src/shared/ReactDOMFlushSync.js
• Added a test for flushSync.

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[CodyJasonBennett]

This is a breaking change, as react-reconciler 0.32 corresponds to React 19.1.

Been thinking on this, since we could risk not supporting 19.x. We can choose to inline if we're sure it is backwards compatible.

[krispya]

That's a good catch. I'll verify this.

[krispya]

I confirmed flushSyncFromReconciler is in v0.31 as well. I think it is safe to use it without inlining. We now have a test for flushSync so going forward we can know if this breaks when updating the reconciler. I'll downgrade the minimum version though as you pointed out.