Refactor: Extract root component architecture and add comprehensive test coverage

[BChoudhury-ms]

Preview this branch

This PR introduces a comprehensive refactoring of the root application architecture to improve maintainability, testing, and separation of concerns.

Changes:

• LoadingExplorer.tsx: Loading state component with proper accessibility features
• ExplorerContainer.tsx: Container component for the main explorer interface with all child components
• Root.tsx: New root component with FluentProvider theme integration and error boundary
• App.tsx: Main application component handling explorer lifecycle, metrics, and conditional rendering
• Main.tsx: Simplified to use the new component architecture with MetricScenarioProvider wrapper
• ContainerCopyPanel.tsx: Minor refactoring for improved structure

Test Coverage:

• Added unit tests for all new components (App.test.tsx, ExplorerContainer.test.tsx, LoadingExplorer.test.tsx, Root.test.tsx)