ProMCDA v2.0.0 - refactor as a Python library

ProMCDA has evolved from a script-based tool into an interactive Python library with a modular structure and enhanced usability.

What's new in v2.0.0:

• Library refactoring: now available as an installable Python package (e.g. import promcda).
• Interactive methods: core MCDA functions are organized into classes and methods for cleaner API usage.
• Example notebooks: two ready-to-use workflows in demo/ and training/, showcasing applications.
• Improved documentation: updated API reference and usage patterns.