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/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)");