fix(auth): reuse a fresh Xbox Live token chain at PLAY instead of refetching it

[xRookieFight]

Summary

• PLAY re-ran the full device/user/XBL/XSTS/SISU chain (eight sequential HTTP round trips) on every launch, even right after _warm_xbox_preauth had just minted the same tokens with hours of validity left — about 10s of every launch's wait spent redoing work that was already done.
• xbl_preauth now reuses the cached online payload when it still clears a 30-minute margin, and only re-runs the chain once that margin is gone (or the cache is missing/stale), so a warm background sign-in actually gets used at PLAY.
• The offline-resilience fallback (a network failure mid-refresh falling back to a still-valid cache) is untouched — it still uses its own thin 60s margin.

Test plan

• python -m pytest tests/test_auth_settings.py tests/test_auth_errors.py -q — added two new tests: a fresh cache skips the network entirely, and a cache below the reuse margin still drives a real refresh.
• python -m pytest tests/ -q — full suite passes (one pre-existing, unrelated failure on this machine from a missing rpm CLI, reproduced on main).