Ingest the tests from CPython

[jaraco]

Closes #2

• Add test_tarfile from Python 3.12.2.
• Add test fixtures from Python 3.12.2
• Override support.findfile to find resources here.
• Explicitly invoke setUpModule/tearDownModule as workaround for setUpModule/tearDownModule not invoked pytest-dev/pytest#12219.
• Restore Python 3.8 compatibility in with expression.
• Use findfile in modules_missing test.
• Ensure backport is used when test_tarfile imports tarfile.
• Backport the archiver_tests.
• Add compatibility shims for os_helper and support.
• Add compatibility shims for catch_warnings.
• Make tests and compat packages
• Add Python 3.9 shims for os_helper migration.
• Add shim for check__all__ compatibility.
• Add shims for Python 3.8 support and warnings modules.
• Add shim for Random.randbytes.
• Add shims for removeprefix and removesuffix.
• Make tarfile a package so it can hold more.
• Add compatibility shim for removesuffix.
• Exclude compat packages from coverage.