Owns the ETS tables that back real-time metering.

This process does nothing on the hot path — it merely creates and owns public, named ETS tables so that writers (AuroraMeter.Counter) and readers hit ETS directly without a GenServer bottleneck:

• :aurora_meter_counters — {tenant_key, feature, bucket} => value, where bucket is a period start (DateTime) or {:day, Date} for history
• :aurora_meter_dirty — counter keys changed since the last database flush
• :aurora_meter_touched — counter keys changed since the last PubSub broadcast
• :aurora_meter_subscription_cache — tenant_key => {subscription, expires_at}

It also listens on the subscription-invalidation PubSub topic so that a plan change applied on any node evicts the cached subscription on every node.

If this process crashes the tables are lost; its supervisor restarts it and the tables are recreated (counter state rehydrates lazily from the database).