fix(authoring): CSV import accepts variable-length arrays; Plain MQTT isArray warns at authoring (lmxopcua#770)

CSV: IsArray with blank/0 ArrayLength is the variable-length shape browse-commit and the composer produce, so its own export now re-imports.
Plain MQTT: MqttTagDefinitionFactory.Inspect (the driver's parse, consulted by the authoring inspector) now advises when isArray is set on a Plain-shaped tag; Sparkplug-shaped blobs stay quiet.
Live Sparkplug array test and SDK reflection items remain open.

Claude-Session: https://claude.ai/code/session_01GT67AEHd2Acv1YPwGfXEoV

tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Uns/RawTagCsvRoundTripTests.cs

@@ -68,6 +68,18 @@ public sealed class RawTagCsvRoundTripTests
         AssertRoundTrip(DriverTypeNames.Galaxy, new[] { galaxy });
     }
 
+    [Fact]
+    public void Variable_length_array_round_trips_lmxopcua_770()
+    {
+        // IsArray with no ArrayLength is what browse-commit and the composer produce (ArrayDimensions=[0]);
+        // the CSV import used to reject its own export.
+        var variable = new RawCsvExportTag(
+            null, "profile", "Float", TagAccessLevel.Read, false, null,
+            """{"nodeId":"nsu=urn:plc;s=Profile","isArray":true}""");
+
+        AssertRoundTrip(DriverTypeNames.OpcUaClient, new[] { variable });
+    }
+
     [Fact]
     public void Export_header_matches_the_driver_column_dictionary()
     {