[Smoke test] Add Network Inspector smoke suite and refactor dispose logic

[EmmaYuan1015]

• Add new NetworkInspectorTest smoke suite to verify Run/Stop Network Inspector commands are visible in the command palette
• Register NetworkInspectorTest in the main smoke entry point
• Refactor CommandPaletteTest, FileExplorerTest, DebugConfigurationTest, and PackagerTest to reuse BaseSmokeTest.initApp/dispose instead of duplicating the app lifecycle boilerplate