[go_router] Add maybePop for safe navigation pops

[muhammadkamel]

Summary

• Adds maybePop to GoRouter, GoRouterDelegate, and GoRouterHelper (context.maybePop()), mirroring Navigator.maybePop and Material BackButton behavior.
• Unlike pop(), maybePop() returns false instead of throwing when nothing can be popped.
• When a pop completes synchronously, maybePop() calls restore() to keep routeInformationProvider in sync with GoRouterDelegate.currentConfiguration (same as pop()).
• Adds test coverage for maybePop, restore(), canPop, mixed Navigator.pop / context.pop flows, and framework BackButton integration.
• Ignores /coverage/ in go_router .gitignore.

Motivation

Apps commonly gate back navigation with if (context.canPop()) context.pop(). Framework widgets like BackButton use Navigator.maybePop(), which is safe but does not sync GoRouter URL/state. maybePop() provides a single GoRouter-native safe pop API:

await context.maybePop();

Test plan

• flutter test packages/go_router/test/maybe_pop_test.dart
• flutter test packages/go_router/test/restore_test.dart
• flutter test packages/go_router/test/extension_test.dart
• flutter test packages/go_router/test/delegate_test.dart
• flutter test packages/go_router/test/router_test.dart

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[gemini-code-assist]

Code Review

This pull request introduces a maybePop method to GoRouter, GoRouterDelegate, and GoRouterHelper to support popping routes without throwing exceptions when the stack is empty, mirroring Navigator.maybePop. It also adds extensive tests covering the new method, state restoration, and integration scenarios. The review feedback suggests adding a state.mounted check within the asynchronous loop in GoRouterDelegate.maybePop to prevent potential exceptions if a navigator is unmounted during execution.

[muhammadkamel]

Hi @chunhtai @hannah-hyj

Would appreciate a review when you have time. Thanks!