Optimize CRUD Table Project: Material 3, Code Quality, Testing & CI #9

This PR addresses a bundle of improvements to modernize and optimize the project as outlined:

1. Material 3 Migration & Dependency Updates

• Upgrade Flutter and Dart SDK constraints in pubspec.yaml (ensure compatibility with latest stable releases)
• Replace old Material widgets with Material 3 variants (FilledButton, improved Card, etc.)
• Update theming to useMaterial3: true
• Refactor example and core widget code to use new widget patterns
• Update screenshots and README for new look

2. Code Quality & Linting

• Enhance analysis_options.yaml to enable stricter lint rules beyond default
• Refactor code for better type safety (use sealed classes for UI/data states)
• Improve code documentation and inline comments

3. Test Coverage

• Add unit and widget tests for core utilities and components
• Add integration tests for CRUD flows

4. Performance Optimizations

• Optimize lazy loading and widget build methods (memoization, const constructors)
• Profile rebuilds and resolve performance bottlenecks (use Flutter DevTools)

5. CI/CD Pipeline

• Add GitHub Actions workflows for CI, static code analysis, and code coverage reporting
• Set up automation for pub.dev publish readiness checks

Related Issues: #6, #7

To Review:

• All impacted files for compatibility and new features
• Ensure that all tests pass and lint warnings are resolved
• Confirm Material 3 visual update in example app

cc @ireshmw