make internal sources ownerless

[Rich-Harris]

WIP fix for #13011. Essentially, all the sources that we create internally (version sources on proxies and reactive sets/maps/etc) need to be ownerless to avoid triggering the self-dependency guard.

One way to do that is to add , null to all the internal source call-sites, which is what I've started doing here. But really, that's backwards — the real (and future-proof) fix is to have an internal representation of $state that is distinct from source. Working on that now

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[Rich-Harris]

One thing I notice: in the case of a state proxy that does not have a top-level source, we don't trigger the guard logic — for example if we tweak the example in #10308

<script>
  let elapsed = $derived.by(() => {
    let object = $state({ seconds: 0 });

    setInterval(() => {
      console.log('incrementing');
      object.seconds += 1;
    }, 1000);

    return object.seconds;
  });
</script>

<p>{elapsed}</p> 

That's true on main as well so I don't think it needs to be fixed as part of this PR, but making a note of it. I guess we'd need to track the owner inside the top-level $.proxy(...) call and apply similar logic inside the get handler or something