review(Driver.Modbus.Addressing): fix misleading byte-order hint + drop dead overflow guard

Re-review at 7286d320. -010 (Low): TryParseByteOrder no longer lists REAL/DINT/UINT as type
codes (gave wrong 'field 2' advice -> second parse error); generic byte-order error instead.
-011 (Low): remove unreachable offsetWithinBank>ushort.MaxValue guard (DecodeOctalVAddress
caps at 0xFFFF). + TDD.

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Modbus.Addressing/DirectLogicAddress.cs

@@ -117,11 +117,12 @@ public static class DirectLogicAddress
 
         // System bank: the registers are contiguous from V40400, so the offset within the bank
         // is the plain decimal distance from the octal base, not another octal decode.
-        var offsetWithinBank = octalValue - SystemVMemoryOctalBase;
-        if (offsetWithinBank > ushort.MaxValue)
-            throw new OverflowException(
-                $"V-memory address '{vAddress}' is outside the addressable system bank");
-        return SystemVMemoryToPdu((ushort)offsetWithinBank);
+        // Driver.Modbus.Addressing-011: the subtraction result is provably <= 0xBEFF because
+        // DecodeOctalVAddress already caps octalValue at 0xFFFF, so no overflow guard is needed
+        // here. The real overflow guard (pdu > ushort.MaxValue) lives in SystemVMemoryToPdu and
+        // is reachable only when that helper is called directly with a large explicit offset.
+        var offsetWithinBank = (ushort)(octalValue - SystemVMemoryOctalBase);
+        return SystemVMemoryToPdu(offsetWithinBank);
     }
 
     // Bit-memory bases per DL260 user manual §I/O-configuration.