Switch to pyproject.toml

[moi15moi]

This PR proposes to replace the existing setup.py file with a pyproject.toml file to modernize the project's build system configuration.

Note that I changed a bit the configuration.
Previously, we had this code to configure the requirements:

if os.environ.get("READTHEDOCS") != "True":
    requirements.extend(
        [
            'pywin32; sys_platform == "win32"',
            'pycairo; sys_platform == "linux" or sys_platform == "darwin"',
            'PyGObject; sys_platform == "linux" or sys_platform == "darwin"',
        ]
    )

Now, it will always install those packages. I don't think it is possible to look to a environment variable with a pyproject.toml configuration file.

[moi15moi]

The macOS and the lint CI fails is unrelated to this PR.

[CoffeeStraw]

Thanks!
I should have fixed CI issues, could you rebase and run them again when you have time?

Also, could you remove the < Python3.9 tags and add 3.11 and 3.12?

[moi15moi]

Done