feat(modbus): String + BitInRegister array decode + equipment-tag arrayLength

- DecodeRegisterArray: add String and BitInRegister cases replacing the
  default:throw; each element decoded by reusing DecodeRegister on its
  contiguous register slice → string[] / bool[]
- ModbusEquipmentTagParser.TryParse: read optional arrayLength key from
  TagConfig JSON and thread it into ModbusTagDefinition.ArrayCount
  (null when absent or zero, preserving scalar behaviour)
- ModbusArrayTests: 8 new tests covering the two decode cases and the
  equipment-tag parser/resolver path; 285/285 green

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Modbus.Contracts/ModbusEquipmentTagParser.cs

@@ -34,9 +34,14 @@ public static class ModbusEquipmentTagParser
             var byteOrder = ReadEnum(root, "byteOrder", ModbusByteOrder.BigEndian);
             var bitIndex = (byte)ReadInt(root, "bitIndex");
             var stringLength = (ushort)ReadInt(root, "stringLength");
+            // isArray / arrayLength — optional keys authored by the typed Modbus tag editor.
+            // When arrayLength > 0 we expose an array tag of that count; otherwise scalar.
+            var arrayLength = ReadInt(root, "arrayLength");
+            int? arrayCount = arrayLength > 0 ? arrayLength : null;
             def = new ModbusTagDefinition(
                 Name: reference, Region: region, Address: (ushort)address, DataType: dataType,
-                Writable: true, ByteOrder: byteOrder, BitIndex: bitIndex, StringLength: stringLength);
+                Writable: true, ByteOrder: byteOrder, BitIndex: bitIndex, StringLength: stringLength,
+                ArrayCount: arrayCount);
             return true;
         }
         catch (JsonException) { return false; }

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Modbus/ModbusDriver.cs

@@ -479,6 +479,25 @@ public sealed class ModbusDriver
                     arr[i] = (double)DecodeRegister(data.AsSpan(i * elementBytes, elementBytes), tag);
                 return arr;
             }
+            case ModbusDataType.String:
+            {
+                // Each element occupies elementRegs registers = elementBytes bytes, encoding
+                // StringLength chars packed high-byte-first or low-byte-first per tag.StringByteOrder.
+                // DecodeRegister handles the per-element slice identically to the scalar path.
+                var arr = new string[count];
+                for (var i = 0; i < count; i++)
+                    arr[i] = (string)DecodeRegister(data.AsSpan(i * elementBytes, elementBytes), tag);
+                return arr;
+            }
+            case ModbusDataType.BitInRegister:
+            {
+                // Each element is 1 holding register (2 bytes). The same BitIndex is applied to
+                // every element. DecodeRegister returns bool for BitInRegister scalar slices.
+                var arr = new bool[count];
+                for (var i = 0; i < count; i++)
+                    arr[i] = (bool)DecodeRegister(data.AsSpan(i * elementBytes, elementBytes), tag);
+                return arr;
+            }
             default:
                 throw new InvalidOperationException(
                     $"Array decode not supported for {tag.DataType} (use scalar tags or split by element)");