Perf/copilot cleanup and optimizations (#2447)

* perf: remove deprecated copilot feature, add ARM timeouts, fix race conditions

- Remove entire QueryCopilot feature (~50 files deleted, ~30 files cleaned)
- Remove CopilotConfigured and SampleDataLoaded metric phases
- Fix DatabaseTreeRendered 76% stuck rate (remove one-shot guard in useMetricPhases)
- Add 8s default timeout to ARM requests (AbortController-based)
- Fix MSAL token forceRefresh (true -> false, use cache)
- Add concurrency limit of 5 to collection loading in Explorer
- Remove orphaned SampleDataClient.ts and queryCopilotSampleData.json
- Clean up dead sampleDataConnectionInfo field from UserContext

* Clean up copilot and optimize initialization

* Clean up copilot and optimize initialization

src/Explorer/SplashScreen/SampleUtil.ts

@@ -31,7 +31,6 @@ export const checkContainerExists = (databaseName: string, containerName: string
   hasContainer(databaseName, containerName, useDatabases.getState().databases);
 
 export enum SampleDataFile {
-  COPILOT = "Copilot",
   FABRIC_SAMPLE_DATA = "FabricSampleData",
   FABRIC_SAMPLE_VECTOR_DATA = "FabricSampleVectorData",
 }
@@ -43,9 +42,6 @@ const containerSettings: {
     indexingPolicy?: DataModels.IndexingPolicy;
   };
 } = {
-  [SampleDataFile.COPILOT]: {
-    partitionKeyString: "category",
-  },
   [SampleDataFile.FABRIC_SAMPLE_DATA]: {
     partitionKeyString: "categoryName",
   },
@@ -120,11 +116,6 @@ export const createContainer = async (
 export const importData = async (sampleDataFile: SampleDataFile, collection: ViewModels.Collection): Promise<void> => {
   let documents: JSONObject[] = undefined;
   switch (sampleDataFile) {
-    case SampleDataFile.COPILOT:
-      documents = (
-        await import(/* webpackChunkName: "queryCopilotSampleData" */ "../../../sampleData/queryCopilotSampleData.json")
-      ).data;
-      break;
     case SampleDataFile.FABRIC_SAMPLE_DATA:
       documents = (await import(/* webpackChunkName: "fabricSampleData" */ "../../../sampleData/fabricSampleData.json"))
         .default;

src/Explorer/SplashScreen/SplashScreen.tsx

@@ -21,7 +21,6 @@ import { Action } from "Shared/Telemetry/TelemetryConstants";
 import { traceOpen } from "Shared/Telemetry/TelemetryProcessor";
 import { useCarousel } from "hooks/useCarousel";
 import { usePostgres } from "hooks/usePostgres";
-import { useQueryCopilot } from "hooks/useQueryCopilot";
 import { ReactTabKind, useTabs } from "hooks/useTabs";
 import * as React from "react";
 import ConnectIcon from "../../../images/Connect_color.svg";
@@ -215,12 +214,6 @@ export const SplashScreen: React.FC<SplashScreenProps> = ({ explorer }) => {
           (state) => state.sampleDataResourceTokenCollection,
         ),
       },
-      {
-        dispose: useQueryCopilot.subscribe(
-          () => setState({}),
-          (state) => state.copilotEnabled,
-        ),
-      },
     );
 
     return () => {