TelemetryRegistry

Ordered registry of Telemetry integrations, keyed by Telemetry.name (re-register replaces, keeping the original position).

Copy-on-write via atomic CAS (the AbortController callback-list idiom): list/get serve the agent hot path from an immutable snapshot, so a concurrent register/clear can never throw ConcurrentModificationException out of a live agent call — telemetry must never alter the loop.