A recorder that records nothing, and says so with an empty schema.

Mirrors tbp/monty/frameworks/models/salience/telemetry.py::NoopSalienceSMTelemetry, which is Monty's default: a config that does not ask for salience telemetry pays nothing for it. state_dict/1 still answers every key, empty, so a consumer indexing the dict works the same either way.