refactor(historian): single-parse ExtractTagHistorize + review-nit tests/docs

Stop parsing TagConfig twice per tag on the deploy hot path: Phase7Composer's
equipment-tag Select lambda is now block-bodied (captures isHistorized/historianTagname
once), and DeploymentArtifact.BuildEquipmentTagPlans captures locals before result.Add.
Add wrong-type-historianTagname InlineData to ExtractTagHistorizeTests. Extend the
parity round-trip fixture with a 4th tag (isHistorized:false + JSON-null tagname)
exercising the artifact-side private guard path. Align DeploymentArtifact's
ExtractTagHistorize doc-comment with the composer-side phrasing (ExtractTagFullName /
ExtractTagAlarm cross-reference).

src/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer/Phase7Composer.cs

@@ -335,18 +335,22 @@ public static class Phase7Composer
             .OrderBy(t => t.EquipmentId, StringComparer.Ordinal)
             .ThenBy(t => t.FolderPath ?? string.Empty, StringComparer.Ordinal) // coalesce so the sort matches the artifact-decode side exactly
             .ThenBy(t => t.Name, StringComparer.Ordinal)
-            .Select(t => new EquipmentTagPlan(
-                TagId: t.TagId,
-                EquipmentId: t.EquipmentId!,
-                DriverInstanceId: t.DriverInstanceId,
-                FolderPath: t.FolderPath ?? string.Empty,
-                Name: t.Name,
-                DataType: t.DataType,
-                FullName: ExtractTagFullName(t.TagConfig),
-                Writable: t.AccessLevel == TagAccessLevel.ReadWrite,
-                Alarm: ExtractTagAlarm(t.TagConfig),
-                IsHistorized: ExtractTagHistorize(t.TagConfig).IsHistorized,
-                HistorianTagname: ExtractTagHistorize(t.TagConfig).HistorianTagname))
+            .Select(t =>
+            {
+                var (isHistorized, historianTagname) = ExtractTagHistorize(t.TagConfig);
+                return new EquipmentTagPlan(
+                    TagId: t.TagId,
+                    EquipmentId: t.EquipmentId!,
+                    DriverInstanceId: t.DriverInstanceId,
+                    FolderPath: t.FolderPath ?? string.Empty,
+                    Name: t.Name,
+                    DataType: t.DataType,
+                    FullName: ExtractTagFullName(t.TagConfig),
+                    Writable: t.AccessLevel == TagAccessLevel.ReadWrite,
+                    Alarm: ExtractTagAlarm(t.TagConfig),
+                    IsHistorized: isHistorized,
+                    HistorianTagname: historianTagname);
+            })
             .ToList();
 
         // Per-equipment tag base = the shared substring-before-first-dot across each equipment's