Performance: SceneDataTransformer always re-runs transformations on activate

[torkelo]

Transformations can be very slow (Especially if they involve parsing dates). Currently SceneDataTransformer does the transformations always on activate which can make going into panel edit and back very slow / sluggish for panels with slow transformations.

This problem can be found here: https://ops.grafana-ops.net/d/b08c039f-9708-4ff6-b62b-48508459be405/reduced-env-to-reproduce-23-87219?orgId=1&scenes&var-unitcost_per_1k=1.32&var-unitcost=0.00132&from=2023-10-31T00:00:00.000Z&to=2024-02-06T12:00:00.000Z

[grafanabot]

🚀 Issue was released in v4.19.0 🚀