refactor: Rename package from password_generator_extended to password_engine

[dhruvanbhalara]

Title

Refactor: Rename package from password_generator_extended to password_engine

Description

This Pull Request renames the entire package to password_engine. This is a comprehensive refactor that touches configuration, documentation, and source code identifiers.

Key Changes

• Configuration:
  • Updated pubspec.yaml name to password_engine.
  • Removed flutter dependency to make it a pure Dart package (supports both Dart and Flutter).
  • Updated description to: "A comprehensive and extensible password generation library for Dart and Flutter".
  • Added new topics: password, security, generator, cryptography, random.
  • Updated homepage URL to point to the new repository location.
• File Structure:
  • Renamed lib/password_generator_extended.dart to lib/password_engine.dart.
  • Renamed test/password_generator_extended_test.dart to test/password_engine_test.dart.
• Source Code:
  • Updated all imports across lib/, test/, and example/ to use package:password_engine/....
• Example App:
  • Renamed example project to password_engine_example.
  • Updated its dependencies and build configuration.
• Documentation:
  • Updated README.md title, installation instructions, and links.
  • Updated CHANGELOG.md.

Why this change?

The previous name, password_generator_extended, felt verbose and implied it was merely an extension of another library.

The new name, password_engine, was chosen to:

1. Reflect Architecture: The library uses a modular Strategy and Estimator pattern. It is not just a function; it is an engine that you configure and drive.
2. Imply Robustness: "Engine" suggests reliability, power, and a core system component, aligning with the use of CSPRNG (Random.secure()) and entropy calculations.
3. Improve Branding: It is short, punchy, and professional (password_engine vs password_generator_extended).
4. Broaden Support: By removing the Flutter dependency, the engine now runs on any Dart platform (CLI, Server, Web), not just Flutter apps.

Verification

• flutter test (Root): All 8 tests passed.
• flutter test (Example): All 23 tests passed.
• pana Analysis: Code score is optimal (deduction only for currently mismatched remote repo URL).