Core: Ensure that simultaneous onStoriesChanged don't clobber each other

[tmeasday]

There was an issue where if you HMR-ed there was a chance that the two calls to onStoriesChanged happened simultaneously, which would end up with 2 storyRenders for the same story that competed with each other.

The net result of that is that args changing would sort of stop working (storyArgsUpdated wasn't emitted).

What I did

Added tests and deal with the case that two renderSelections happen simultaneous (without a change of story - see #17599 for that case).

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[tmeasday]

I'm really unsure why the logic wouldn't have applied in the aborted cased too (the lastRender is out of date no matter what!). The tests from the PR that added this code #17599 still pass so I think it's good.

[nx-cloud]

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