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/Tabs/QueryTab/QueryTab.tsx

@@ -1,19 +1,12 @@
 import { sendMessage } from "Common/MessageHandler";
 import { ActionType, OpenQueryTab, TabKind } from "Contracts/ActionContracts";
 import { MessageTypes } from "Contracts/MessageTypes";
-import { CopilotProvider } from "Explorer/QueryCopilot/QueryCopilotContext";
-import { userContext } from "UserContext";
 import React from "react";
 import * as DataModels from "../../../Contracts/DataModels";
 import type { QueryTabOptions } from "../../../Contracts/ViewModels";
 import { useTabs } from "../../../hooks/useTabs";
 import Explorer from "../../Explorer";
-import {
-  IQueryTabComponentProps,
-  ITabAccessor,
-  QueryTabComponent,
-  QueryTabCopilotComponent,
-} from "../../Tabs/QueryTab/QueryTabComponent";
+import { IQueryTabComponentProps, ITabAccessor, QueryTabComponent } from "../../Tabs/QueryTab/QueryTabComponent";
 import TabsBase from "../TabsBase";
 
 export interface IQueryTabProps {
@@ -80,13 +73,7 @@ export class NewQueryTab extends TabsBase {
   }
 
   public render(): JSX.Element {
-    return userContext.apiType === "SQL" ? (
-      <CopilotProvider>
-        <QueryTabCopilotComponent {...this.iQueryTabComponentProps} />
-      </CopilotProvider>
-    ) : (
-      <QueryTabComponent {...this.iQueryTabComponentProps} />
-    );
+    return <QueryTabComponent {...this.iQueryTabComponentProps} />;
   }
 
   public onActivate(): void {