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

src/ZB.MOM.WW.ScadaBridge.Commons/Types/AttributeValueCodec.cs

@@ -72,6 +72,8 @@ public static class AttributeValueCodec
     private static object? ParseScalar(string? s, DataType t)
     {
         if (s is null) throw new FormatException("List elements may not be null.");
+        if (!IsValidElementType(t))
+            throw new FormatException($"Unsupported list element type '{t}'.");
         var c = CultureInfo.InvariantCulture;
         try
         {