refactor(password-engine): migrate dependency to pub.dev and stabilize tests

[dhruvanbhalara]

Description

Migrate password_engine from git source to pub.dev and align the app integration with the new service abstraction. This PR also includes compatibility fixes required to keep tests green after the migration (localization key alignment, updated generator state test types, and strategy test expectation updates).

Related Issues

N/A

Type of Change

• 🐛 Bug fix (non-breaking change which fixes an issue)
• ✨ New feature (non-breaking change which adds functionality)
• 💥 Breaking change (fix or feature that would cause existing functionality to not work as expected)
• 📝 Documentation update
• 🎨 UI/UX refinement

Checklist

• I have followed the project's CONTRIBUTING.md guidelines.
• My code follows the style guidelines of this project.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes.
• Any dependent changes have been merged and published in downstream modules.

Screenshots (if applicable)

N/A

Testing Instructions

1. Run flutter pub get.
2. Run flutter analyze.
3. Run flutter test.
4. Verify no dependency resolution conflict occurs for password_engine + hive_ce_generator.

📊 Code Coverage Report

Metric	Value
Total Lines	4631
Lines Hit	3700
Overall Coverage	79.90%

Generated by PassVault CI