Add pyproject.toml for compatability with pip 25

[jank324]

Description

Adds a pyproject.toml to support the modern editable build mode and configure setuptools as the build system.

Motivation and Context

• I have raised an issue to propose this change (required for new features and bug fixes)

Closes #245.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation (update in the documentation)

Checklist

• I have updated the changelog accordingly (required).
• My change requires a change to the documentation.
• I have updated the tests accordingly (required for a bug fix or a new feature).
• I have updated the documentation accordingly.
• I have reformatted the code and checked that formatting passes (required).
• I have have fixed all issues found by flake8 (required).
• I have ensured that all pytest tests pass (required).
• I have run pytest on a machine with a CUDA GPU and made sure all tests pass (required).
• I have checked that the documentation builds (required).

Note: We are using a maximum length of 88 characters per line.

[Hespe]

Just to be sure: this minimal project file is sufficient to point pip to setuptools and allow for editable installs? We do not have to move all package metadata out of setup.py into the new file?

[jank324]

At least this is the minimal change suggested in pypa/pip#11457.