Update Lib set, type, and resource concurrency tests to Python 3.15 - #9435

Summary

Sync three previously missing Python 3.15 canonical free-threading suites: set operations, type mutation/cache behavior, and read-only resource accounting.

All three files were migrated with scripts/update_lib migrate from CPython d220409a13b77de7a6c30abe16ea90db01528edc and are byte-identical. This adds 468 lines with 14 test method definitions (approximately 17 cases including inherited set cases; static count, not runtime discovery). No new markers, assertion changes, native changes, or duplicated package initializer.

Validation and limits

• Updater unit tests: 228 passed. Applicable configured hooks and diff checks passed.
• Native API, container-reference lifetime, and type-lock/cache paths were source-reviewed. No local concurrency tests or native build were run; hosted CI must establish runtime results.
• RustPython passes the package GIL-disabled gate; existing threading and platform capability gates still apply.
• Set tests use up to 11 workers. Several workers terminate only after another worker successfully sets an event; two-second barriers and direct joins can fail or strand workers if those paths fail.
• Type tests cover cache monotonicity, class/base/name updates, and special-method propagation to 100 subclasses. The seven-thread regression has six variable-work actors until 200 base changes complete, so allocation/work is scheduling-dependent. The first cache test does not read submitted future results; it is not strong worker-exception coverage.
• Resource coverage is read-only: 10 workers each perform 1,000 empty iterations and two getrusage calls, followed by one process-level call. No resource limits are changed. Canonical feature gates and timing/accounting inequalities are retained unchanged.
• Existing CI's 600-second test timeout provides outer containment, not a deadlock-freedom or general CPython concurrency-equivalence guarantee.

The known native prerequisites for other missing suites remain separate; this PR does not add skip-only unsupported fixture families.