Add deep link bootstrap provider to catch initial route on iOS/Android

[FeodorFitsner]

Summary by Sourcery

Handle platform deep links at app cold start and ensure they initialize the Flet router with a normalized initial route.

New Features:

• Add a deep link bootstrap helper to capture and replay initial route information before the Flet router is mounted.
• Introduce a custom route information provider that normalizes external deep link URIs into Flet's path-based routing format.
• Expose the deep linking bootstrap utility through the main Flet Dart library API.
• Add a Python declarative example app demonstrating a dialog-based component with async data loading.

Enhancements:

• Wire the new route information provider into MaterialApp.router and CupertinoApp.router initialization so initial and subsequent routes use the normalized format.

[sourcery-ai]

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