feat(lmxproxy): add DatetimeArray proto type for DateTime[] round-trip fidelity

Added DatetimeArray message (repeated int64, UTC ticks) to proto and
code-first contracts. Host serializes DateTime[] → DatetimeArray.
Client deserializes DatetimeArray → DateTime[] (not raw long[]).
Client ExtractArrayValue now unpacks all array types including DateTime.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

lmxproxy/src/ZB.MOM.WW.LmxProxy.Client/Domain/ScadaContracts.cs

@@ -120,6 +120,9 @@ public class ArrayValue
 
     [DataMember(Order = 6)]
     public StringArray? StringValues { get; set; }
+
+    [DataMember(Order = 7)]
+    public DatetimeArray? DatetimeValues { get; set; }
 }
 
 [DataContract]
@@ -164,6 +167,13 @@ public class StringArray
     public List<string> Values { get; set; } = [];
 }
 
+[DataContract]
+public class DatetimeArray
+{
+    [DataMember(Order = 1)]
+    public List<long> Values { get; set; } = [];
+}
+
 // ────────────────────────────────────────────────────────────────
 // Quality Code (v2)
 // ────────────────────────────────────────────────────────────────

lmxproxy/src/ZB.MOM.WW.LmxProxy.Client/LmxProxyClient.cs

@@ -271,12 +271,30 @@ public partial class LmxProxyClient : ILmxProxyClient
             TypedValueCase.StringValue => tv.StringValue,
             TypedValueCase.BytesValue => tv.BytesValue,
             TypedValueCase.DatetimeValue => new DateTime(tv.DatetimeValue, DateTimeKind.Utc),
-            TypedValueCase.ArrayValue => tv.ArrayValue,
+            TypedValueCase.ArrayValue => ExtractArrayValue(tv.ArrayValue),
             TypedValueCase.None => null,
             _ => null
         };
     }
 
+    internal static object? ExtractArrayValue(ArrayValue? av)
+    {
+        if (av is null) return null;
+        if (av.BoolValues is not null) return av.BoolValues.Values.ToArray();
+        if (av.Int32Values is not null) return av.Int32Values.Values.ToArray();
+        if (av.Int64Values is not null) return av.Int64Values.Values.ToArray();
+        if (av.FloatValues is not null) return av.FloatValues.Values.ToArray();
+        if (av.DoubleValues is not null) return av.DoubleValues.Values.ToArray();
+        if (av.StringValues is not null) return av.StringValues.Values.ToArray();
+        if (av.DatetimeValues is not null)
+        {
+            return av.DatetimeValues.Values
+                .Select(ticks => new DateTime(ticks, DateTimeKind.Utc))
+                .ToArray();
+        }
+        return null;
+    }
+
     private async Task<T> ExecuteWithRetry<T>(Func<Task<T>> operation, CancellationToken ct)
     {
         if (_resiliencePipeline is not null)