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

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Sql/SqlDriver.cs

@@ -2,6 +2,7 @@ using System.Data.Common;
 using System.Diagnostics.CodeAnalysis;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Logging.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Commons.Observability;
 using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
 using ZB.MOM.WW.OtOpcUa.Driver.Sql.Contracts;
 
@@ -228,7 +229,12 @@ public sealed class SqlDriver
             onChange: (handle, tagRef, snapshot) =>
                 OnDataChange?.Invoke(this, new DataChangeEventArgs(handle, tagRef, snapshot)),
             onError: HandlePollError,
-            backoffCap: PollBackoffCap);
+            backoffCap: PollBackoffCap,
+            // 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.Sql),
+                new KeyValuePair<string, object?>("driver.instance", driverInstanceId)));
     }
 
     /// <summary>