Replace setup.py with pyproject.toml

[PennyHow]

pyproject.toml is the new standardised format for packaging, which is easier to work with and allows more sophisticated configurations compared to setup.py. So we should look at updating our setup.py to a pyproject.toml file instead.

https://packaging.python.org/en/latest/guides/writing-pyproject-toml/#writing-pyproject-toml