Migrating setup.py to pyproject.toml

[runora95]

Context:
The build and installation methods using setup.py have been deprecated; pyproject.toml is the recommended method. Pennylane needs to be updated to use pyproject.toml instead.

Description of the Change:
Update pyproject.toml to be used to build packages

Benefits:
setup.py is deprecated, this change ensures that packages can still be built

Possible Drawbacks:

Related GitHub Issues:

[github-actions]

Hello. You may have forgotten to update the changelog!
Please edit doc/releases/changelog-dev.md with:

• A one-to-two sentence description of the change. You may include a small working example for new features.
• A link back to this PR.
• Your name (or GitHub username) in the contributors section.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.69%. Comparing base (5a28158) to head (f6eedec).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #7375   +/-   ##
=======================================
  Coverage   99.69%   99.69%           
=======================================
  Files         529      529           
  Lines       50610    50610           
=======================================
  Hits        50455    50455           
  Misses        155      155           

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[rashidnhm]

Though CI is passing, it seems there are some deprecation warnings being raised by uv, we may want to address those as part of this PR.

https://github.com/PennyLaneAI/pennylane/actions/runs/14887842195/job/41812184792?pr=7375#step:9:17

/home/runner/work/_temp/setup-uv-cache/builds-v0/.tmptnMJ7R/lib/python3.10/site-packages/setuptools/config/_apply_pyprojecttoml.py:82: SetuptoolsDeprecationWarning: `project.license` as a TOML table is deprecated
!!

        ********************************************************************************
        Please use a simple string containing a SPDX expression for `project.license`. You can also use `project.license-files`. (Both options available on setuptools>=77.0.0).

        By 2026-Feb-[18](https://github.com/PennyLaneAI/pennylane/actions/runs/14887842195/job/41812184792?pr=7375#step:9:19), you need to update your project and remove deprecated calls
        or your builds will no longer be supported.

        See https://packaging.python.org/en/latest/guides/writing-pyproject-toml/#license for details.
        ********************************************************************************

!!
  corresp(dist, value, root_dir)
/home/runner/work/_temp/setup-uv-cache/builds-v0/.tmptnMJ7R/lib/python3.10/site-packages/setuptools/config/_apply_pyprojecttoml.py:61: SetuptoolsDeprecationWarning: License classifiers are deprecated.
!!

        ********************************************************************************
        Please consider removing the following classifiers in favor of a SPDX license expression:

        License :: OSI Approved :: Apache Software License

        See https://packaging.python.org/en/latest/guides/writing-pyproject-toml/#license for details.
        ********************************************************************************

!!
  dist._finalize_license_expression()
/home/runner/work/_temp/setup-uv-cache/builds-v0/.tmptnMJ7R/lib/python3.10/site-packages/setuptools/dist.py:761: SetuptoolsDeprecationWarning: License classifiers are deprecated.
!!

        ********************************************************************************
        Please consider removing the following classifiers in favor of a SPDX license expression:

        License :: OSI Approved :: Apache Software License

        See https://packaging.python.org/en/latest/guides/writing-pyproject-toml/#license for details.
        ********************************************************************************

!!

[rashidnhm]

The entire content of this file should be:

from setuptools import setup

setup()

Everything in between is not needed

[rashidnhm]

Suggested change

	requires = ["setuptools>=75", "tomli"]
	requires = ["setuptools>=75.8.1", "tomli"]

setuptools < 75.8.1 may cause build failures, hence why we explicitly pin it explicitly in CI (See #7005)

Also, does PL need tomli as a build dependency?