Update .gitignore and add MIT license metadata for packaging

[francescobianco]

This pull request introduces licensing information for the project and updates the project metadata to reflect the use of the MIT License. The main changes are the addition of a LICENSE file, updates to pyproject.toml to declare the license, and improved packaging metadata.

Licensing and metadata updates:

• Added a new LICENSE file containing the MIT License text.
• Updated pyproject.toml to specify license = "MIT" and added relevant license and Python version classifiers for PyPI.
• Configured setuptools in pyproject.toml to include the LICENSE file in source distributions via the license-files setting.