Adopt dynamic versioning and pyproject.toml for package setup

[EwoutH]

This commit transitions the package setup process from a traditional setup.py-based approach to a modern pyproject.toml configuration. It introduces dynamic versioning to automatically determine the package version from uxsim/__init__.py, eliminating the need for direct imports in the setup phase. This change resolves the import issue encountered during installation and aligns with best practices for Python packaging.

• Added pyproject.toml with build system requirements, project metadata, dependencies, and dynamic versioning configuration.
• Removed direct import of uxsim in setup.py to avoid installation errors.
• Ensured uxsim/__init__.py defines __version__ for dynamic versioning compatibility.

This also fixes local installations failing and adds instruction to the Readme how to install from a git branch.

[toruseo]

Thanks for this, but sorry, I am not familiar with modern packaging practice. Please give me some time to update my knowledge. After that I will do it by my own.

[EwoutH]

Okay, that sounds smart!

This is a good read: https://packaging.python.org/en/latest/guides/writing-pyproject-toml/