* Migrates to pyproject.toml

Switches the build system from setup.py to pyproject.toml.

This change standardizes the project's build configuration,
improves dependency management, and prepares the project for
future enhancements.
Removes unused requirements file.

* Updates minimum Python version

Corrects the minimum Python version specified in pyproject.toml.

The project now requires Python 3.10 or higher.

* Uses installable package for dev dependencies

Updates the installation of development dependencies in the linting workflow to use the installable package.

This simplifies dependency management and aligns with standard Python packaging practices.

* Adds pyupgrade as a dev dependency

Adds `pyupgrade` to the development dependencies.
This enables developers to automatically upgrade Python syntax
to more modern versions, improving code maintainability
and readability.