build: stop pulling setuptools into runtime dependencies

[federicobond]

setuptools was listed in requirements.txt and thus propagated to install_requires, forcing it as a runtime dependency for downstream installs even though it is never imported at runtime.

Remove it from requirements.txt and instead declare it as a build-time requirement only.

[Copilot]

Pull request overview

This PR updates the package’s dependency metadata so that setuptools is no longer propagated as a runtime requirement to downstream consumers, while still ensuring it is available for build-time packaging.

Changes:

• Removed setuptools from requirements.txt so it no longer ends up in install_requires.
• Added a PEP 517 [build-system] section to pyproject.toml to declare setuptools as a build requirement.

Reviewed changes

Copilot reviewed 1 out of 2 changed files in this pull request and generated 1 comment.

File	Description
requirements.txt	Removes setuptools from the dependency list that is used to populate runtime install_requires.
pyproject.toml	Declares setuptools as the PEP 517 build backend requirement (but currently missing wheel).

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[federicobond]

responses should also be dropped from runtime dependencies (it's already in requirements.test.txt)