ScopedStore wraps Store and auto-prefixes groups with a namespace to
prevent key collisions across tenants. QuotaConfig enforces per-namespace
MaxKeys and MaxGroups limits (zero = unlimited). Upserts and expired
keys are excluded from quota counts.
New Store methods: CountAll(prefix) and Groups(prefix) for cross-group
queries. All 93 tests pass with race detector, coverage 94.7%.
Co-Authored-By: Virgil <virgil@lethean.io>
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>