StateTimeline: Complete E2E tests and add simple StateTimelineTooltip unit tests (#112901)

* StateTimeline: E2E tests for basic rendering, no data, and tooltip interactions

* Add tests for StateTimelineTooltip sub-component

* Remove unused import from state-timeline.spec.ts

* updates from PR review

apps/dashboard/pkg/migration/testdata/dev-dashboards-output/panel-timeline/timeline-thresholds-mappings.v42.json

@@ -1069,6 +1069,74 @@
       ],
       "title": "boolean values from data",
       "type": "state-timeline"
+    },
+    {
+      "id": 15,
+      "type": "state-timeline",
+      "title": "no data",
+      "gridPos": {
+        "x": 18,
+        "y": 18,
+        "h": 9,
+        "w": 6
+      },
+      "fieldConfig": {
+        "defaults": {
+          "custom": {
+            "lineWidth": 0,
+            "fillOpacity": 70,
+            "spanNulls": false,
+            "insertNulls": false,
+            "hideFrom": {
+              "tooltip": false,
+              "viz": false,
+              "legend": false
+            },
+            "axisPlacement": "auto"
+          },
+          "color": {
+            "mode": "palette-classic"
+          },
+          "mappings": [],
+          "thresholds": {
+            "mode": "absolute",
+            "steps": [
+              {
+                "color": "green"
+              }
+            ]
+          },
+          "fieldMinMax": false
+        },
+        "overrides": []
+      },
+      "pluginVersion": "12.3.0-pre",
+      "targets": [
+        {
+          "scenarioId": "random_walk",
+          "refId": "A",
+          "seriesCount": 0
+        }
+      ],
+      "datasource": {
+        "type": "grafana-testdata-datasource"
+      },
+      "options": {
+        "mergeValues": true,
+        "showValue": "auto",
+        "alignValue": "center",
+        "rowHeight": 0.9,
+        "legend": {
+          "showLegend": true,
+          "displayMode": "list",
+          "placement": "bottom"
+        },
+        "tooltip": {
+          "mode": "single",
+          "sort": "none",
+          "hideZeros": false
+        }
+      }
     }
   ],
   "preload": false,
@@ -1092,4 +1160,4 @@
   "title": "StateTimeline - Thresholds \u0026 Mappings",
   "uid": "Kce7z9TVz",
   "weekStart": ""
-}
+}