Per-driver counters surfaced via DriverHealth.Diagnostics for the
driver-diagnostics RPC. New OpcUaClientDiagnostics tracks
PublishRequestCount, NotificationCount, NotificationsPerSecond (5s-half-life
EWMA), MissingPublishRequestCount, DroppedNotificationCount,
SessionResetCount and LastReconnectUtcTicks via Interlocked on the hot path.
DriverHealth gains an optional IReadOnlyDictionary<string,double>?
Diagnostics parameter (defaulted null for back-compat with the seven other
drivers' constructors). OpcUaClientDriver wires Session.Notification +
Session.PublishError on connect and on reconnect-complete (recording a
session-reset there); GetHealth snapshots the counters on every poll so the
RPC sees fresh values without a tick source.
Tests: 11 new OpcUaClientDiagnosticsTests cover counter increments, EWMA
convergence, snapshot shape, GetHealth integration, and DriverHealth
back-compat. Full OpcUaClient.Tests 115/115 green.
Closes#276
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
