feat(drivers): per-driver poll-overrun meter on the shared OtOpcUa Meter; NoteOverrun + backoffCap doc notes

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.S7/S7Driver.cs

@@ -3,6 +3,7 @@ using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Logging.Abstractions;
 using S7.Net;
 using S7NetDataType = global::S7.Net.DataType;
+using ZB.MOM.WW.OtOpcUa.Commons.Observability;
 using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
 
 namespace ZB.MOM.WW.OtOpcUa.Driver.S7;
@@ -69,7 +70,12 @@ public sealed class S7Driver
             minInterval: TimeSpan.FromMilliseconds(100),
             onError: HandlePollError,
             backoffCap: TimeSpan.FromSeconds(30),
-            onBatch: (handle, items) => OnDataChangeBatch?.Invoke(this, new DataChangeBatchEventArgs(handle, items)));
+            onBatch: (handle, items) => OnDataChangeBatch?.Invoke(this, new DataChangeBatchEventArgs(handle, items)),
+            // The engine owns no Meter (Core.Abstractions takes no metrics dependency), so this
+            // closure IS the production consumer of its overrun signal.
+            onOverrun: _ => OtOpcUaTelemetry.PollOverruns.Add(1,
+                new KeyValuePair<string, object?>("driver.type", DriverTypeNames.S7),
+                new KeyValuePair<string, object?>("driver.instance", driverInstanceId)));
     }
     // ---- ISubscribable + IHostConnectivityProbe state ----