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/Shared/AppStatePersistenceUtility.ts

@@ -8,7 +8,6 @@ import * as TelemetryProcessor from "../Shared/Telemetry/TelemetryProcessor";
 export enum AppStateComponentNames {
   DocumentsTab = "DocumentsTab",
   MostRecentActivity = "MostRecentActivity",
-  QueryCopilot = "QueryCopilot",
   DataExplorerAction = "DataExplorerAction",
   SelectedRegionalEndpoint = "SelectedRegionalEndpoint",
 }

src/Shared/StorageUtility.ts

@@ -17,7 +17,6 @@ export enum StorageKey {
   MaxWaitTimeInSeconds,
   AutomaticallyCancelQueryAfterTimeout,
   ContainerPaginationEnabled,
-  CopilotSampleDBEnabled,
   CustomItemPerPage,
   DatabaseAccountId,
   EncryptedKeyToken,

src/Shared/Telemetry/TelemetryConstants.ts

@@ -136,13 +136,7 @@ export enum Action {
   LaunchUITour,
   CancelUITour,
   CompleteUITour,
-  OpenQueryCopilotFromSplashScreen,
-  OpenQueryCopilotFromNewQuery,
-  ActivateQueryCopilot,
-  DeactivateQueryCopilot,
-  QueryGenerationFromCopilotPrompt,
   QueryEdited,
-  ExecuteQueryGeneratedFromQueryCopilot,
   DeleteDocuments,
   ReadPersistedTabState,
   SavePersistedTabState,
@@ -157,11 +151,6 @@ export enum Action {
   ConfigurePortal,
   FetchAccountKeys,
   AcquireMsalToken,
-  UpdateCopilotContext,
-  GetCopilotEnabled,
-  CheckCopilotFeatureRegistration,
-  UpdateSampleDataContext,
-  RefreshSampleData,
   ReadDatabases,
   ReadCollections,
   LoadCollectionsPerDatabase,