Portable Athena observability primitives.
This crate owns the reusable observability domain that can be shared across
the Athena server runtime, future adapters, and helper binaries without
depending on Actix, AppState, or route-local database registries.
The current scope covers:
- in-memory metrics state and classification helpers,
- batched client statistics writes,
- optional Linux NDJSON log sinks for gateway traffic,
- reusable gateway log contracts, redaction helpers, and trace emitters.