Create stub for root pyproject editable build

[StafaH]

Description

Create a stub so that the root pyproject can be treated as a package so users can editable install the test package bundle.

Checklist

• I have read and understood the contribution guidelines
• I have run the pre-commit checks with ./isaaclab.sh --format
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• I have updated the changelog and the corresponding version in the extension's config/extension.toml file
• I have added my name to the CONTRIBUTORS.md or my name already exists there

[greptile-apps]

Greptile Summary

This PR makes the repository root available as an empty editable package. The main changes are:

• Adds a setuptools PEP 517 build backend.
• Disables package and module discovery for the root distribution.

Confidence Score: 5/5

This looks safe to merge.

• The empty package configuration matches the stated purpose.
• No concrete build, runtime, or security issue was found in the changed code.

Important Files Changed

Filename	Overview
pyproject.toml	Adds an intentionally empty setuptools build configuration for editable root installs.

_{Reviews (1): Last reviewed commit: "Fix issue with pip install for test" | Re-trigger Greptile}