Dashboards: Node graph panel flickers on each refresh

### What happened? The Node graph panel flickers every time the dashboard auto-refreshes. The entire visualization is cleared and redrawn, causing all nodes and edges to disappear briefly before reappearing. This creates a disruptive user experience when monitoring constant/static data. Can be observed also on play.grafana.org: https://github.com/user-attachments/assets/1cff5c49-454f-4f2d-835c-831ff6d99f4e ### What did you expect to happen? When data hasn't changed between refreshes, the Node graph panel should maintain the current visualization without flickering. The panel should smoothly update or remain static if the data is identical, similar to how other panel types handle refresh cycles with unchanged data. ### Did this work before? No ### How do we reproduce it? 1. Create a dashboard with a Node graph panel and constant data. 2. Set dashboard auto-refresh to 5 seconds 3. Observe the panel - it flickers (clears and redraws) every 5 seconds ### Is the bug inside a dashboard panel? | Key | Value | |--|--| | Panel | nodeGraph @ 12.3.0-18255337623 | | Grafana | Grafana Cloud (fast) // Cloud Advanced | <details><summary>Panel debug snapshot dashboard</summary> ```json { "panels": [ { "id": 2, "type": "nodeGraph", "title": "Reproduced with embedded data", "gridPos": { "h": 13, "w": 15, "x": 0, "y": 0 }, "fieldConfig": { "defaults": {}, "overrides": [] }, "pluginVersion": "12.3.0-18255337623", "targets": [ { "refId": "A", "datasource": { "type": "grafana", "uid": "grafana" }, "queryType": "snapshot", "snapshot": [ { "schema": { "meta": { "preferredVisualisationType": "nodeGraph" }, "name": "nodes", "fields": [ { "name": "id", …