fix(multivalue): Wave-2 review fixes (MV-2/MV-4/MV-12)

- MV-2: guard unsupported element type before parse (no misleading re-wrap); add Float round-trip test
- MV-4: carry ElementDataType through the two validation-flatten ResolvedAttribute sites (ManagementActor.HandleValidateTemplate, BundleImporter.BuildFlattenedConfigForValidation) so MV-5 validation sees element type via every entry point
- MV-12: include ElementDataType in TemplateAttribute add/update audit payloads + fix stale docstring

tests/ZB.MOM.WW.ScadaBridge.Commons.Tests/Types/AttributeValueCodecTests.cs

@@ -49,6 +49,14 @@ public class AttributeValueCodecTests
         Assert.Equal("[\"ACME, Inc.\"]",
             AttributeValueCodec.Encode(new List<string> { "ACME, Inc." }));
 
+    [Fact]
+    public void RoundTrip_FloatList()
+    {
+        var json = AttributeValueCodec.Encode(new List<float> { 1.5f, 2.25f, -3.75f });
+        var back = (IList<float>)AttributeValueCodec.Decode(json, DataType.List, DataType.Float)!;
+        Assert.Equal(new[] { 1.5f, 2.25f, -3.75f }, back);
+    }
+
     [Fact]
     public void Encode_DoubleList_IsInvariant()
     {