feat: add 6 essential mobile-first hooks for modern Flutter apps

[wasabeef]

🚀 Overview

This PR introduces 6 essential mobile-first hooks that address common patterns in modern Flutter app development. These hooks provide
production-ready solutions for async operations, form management, infinite scrolling, and keyboard handling.

✨ New Hooks

Async Operations

• useAsync - Automatically executes async operations with built-in loading, error, and data states
• useAsyncFn - Manually controlled async operations perfect for user-triggered actions like form submissions

UI Interactions

• useDebounceFn - Type-safe debounced function execution for search inputs and API calls
• useKeyboard - Tracks keyboard visibility and dimensions for responsive layouts

Data Management

• useForm - Comprehensive form state management with validation, dirty tracking, and submission handling
• useInfiniteScroll - Automatic scroll-based data loading with pagination support

📋 Why These Hooks?

These hooks address the most common mobile app patterns:

• API Integration: Handle loading states, errors, and data fetching elegantly
• User Input: Debounce search queries and validate forms with minimal boilerplate
• Performance: Efficient infinite scrolling and keyboard-aware layouts
• Developer Experience: Type-safe, well-tested, and thoroughly documented

💡 Usage Examples

// Async data fetching
final userState = useAsync(() => fetchUserData());
if (userState.loading) return CircularProgressIndicator();
if (userState.hasError) return Text('Error: ${userState.error}');
return UserProfile(user: userState.data!);

// Form with validation
final form = useForm({
  'email': useField(validators: [Validators.required(), Validators.email()]),
  'password': useField(validators: [Validators.minLength(8)]),
});

// Infinite scroll
final scroll = useInfiniteScroll(
  loadMore: () async {
    final items = await api.fetchItems(page: currentPage);
    return items.length >= pageSize;
  },
);

📚 Documentation

- Comprehensive DartDoc comments with examples
- Dedicated documentation files in /docs
- Interactive demos for each hook
- Integration with the main demo app

✅ Testing

- 100% test coverage for all new hooks
- Edge cases and error scenarios covered
- Consistent with existing test patterns

🏗️ Architecture

- Followed existing patterns (e.g., useAsyncFn in separate file like other Fn-suffix hooks)
- Extracted shared AsyncState class to avoid duplication
- Maintained backward compatibility (except for the breaking change below)

⚠️ Breaking Changes

- Removed flutter_hooks_testing.dart in favor of inline testing utilities. This file was not part of the public API and was only used
internally for tests.

📝 Checklist

- All tests pass (252 tests passing)
- Documentation added for all public APIs
- Demo examples created
- Code follows existing patterns and conventions
- No linting issues
- README updated with new hooks