Improve integration test options

[joerick]

Apologies for another 3.x PR, this has been sitting in my local repo for a few days so I thought I'd polish it up.

Essentially, I find myself setting CIBW_ENABLE and CIBW_PLATFORM locally to run integration tests more and more, but as discussed previously, it's not very user friendly.

This necessitates a change from the utils.platform variable we had before to a utils.get_platform() function. But I think it's worth it, it also means we're not duplicating state between os.environ and utils.platform.

[Copilot]

Pull Request Overview

This PR improves the integration testing experience by replacing the static utils.platform attribute with the dynamic utils.get_platform() function. Key changes include updating all platform checks across test files, adding new pytest options in conftest.py for --platform and --enable, and updating documentation and CI workflows to reflect these changes.

Reviewed Changes

Copilot reviewed 24 out of 24 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
test/test_pep518.py	Updated platform checks to use utils.get_platform().
test/test_musllinux_X_Y_only.py	Switched from utils.platform to utils.get_platform() for Linux testing.
test/test_manylinuxXXXX_only.py	Replaced platform check with a call to utils.get_platform().
test/test_macos_archs.py	Updated multiple macOS platform checks to use utils.get_platform().
test/test_linux_python.py	Updated Linux platform check to use utils.get_platform().
test/test_ios.py	Replaced utils.platform with utils.get_platform() in iOS-specific tests.
test/test_environment.py	Replaced platform attribute references with utils.get_platform().
test/test_emulation.py	Updated the platform check to use utils.get_platform().
test/test_dependency_versions.py	Updated platform-condition checks to utilize utils.get_platform().
test/test_cpp_standards.py	Updated platform check for C++ standards and noted a digit separator usage.
test/test_container_images.py	Replaced linux platform check with utils.get_platform().
test/test_container_engine.py	Updated tests to use utils.get_platform() for Linux environment checks.
test/test_build_frontend_args.py	Replaced platform check with a call to utils.get_platform().
test/test_before_test.py	Updated platform check to use utils.get_platform() in test setup.
test/test_before_build.py	Replaced utils.platform with utils.get_platform() in build-related tests.
test/test_abi_variants.py	Updated platform checks to use utils.get_platform() in ABI tests.
test/test_0_basic.py	Changed enable group extraction to use utils.get_enable_groups().
test/conftest.py	Updated platform-related logic and added new pytest option parsing.
docs/contributing.md	Updated instructions to reflect the new --platform and --enable options.
.github/workflows/test.yml	Updated the DEFAULT_CIBW_ENABLE import to use test.utils as per changes.

Comments suppressed due to low confidence (1)

test/test_cpp_standards.py:81

• [nitpick] If the digit separator (100'000) is intentional as a readability aid, consider adding a brief comment to clarify its purpose and ensure consistency with other numeric literals.

cpp14_project.template_context["spam_cpp_top_level_add"] = "int a = 100'000;"