fix(tracemetrics): Store label format of equation so duplicates aren't clobbered

[narsaynorath]

There's a subtle bug that users were seeing when creating metrics equations in alerts. If you first added two metric queries to your equation that were the same, and then changed a filter or aggregate on one of them, the change would not update properly (i.e the equation would have stale references even though the subcomponent queries UI was updated)

To mitigate this, I've opted to add some more metadata to the VisualizeEquation class about the internal state for the VisualizeEquation. By doing this, we have a stronger method of updating the equation. Previously there was a subtle de-dupe happening with references (which is why the trigger was two of the same metric query). With the internal state stored on the class, the utils for synchronizing changes from the metric queries to the equation can change the correct queries.

As an example, set something up vaguely like this on Explore, Alerts, or Dashboards:
query A: count()
query B: count()
equation: A + B (resolves to count() + count())

Since the synchronization calls take the expression count() + count() and unresolve (i.e. change it back to label format so we can operate on the references), it actually loses A + B and thinks it's working with A + A so changes to B were silently dropped and changes to query A duplicate across both references. Storing the internal state is important to keep this context and avoid re-computing it when unnecessary.

[narsaynorath]

@cursor review

[narsaynorath]

@cursor review

[cursor]

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