Task #137 — Modbus per-tag suffix grammar (type / bit / byte-order / array)

Adds the full Wonderware/Kepware/Ignition-style address suffix grammar so
users paste tag spreadsheets without per-tag manual translation:

  <region><offset>[.<bit>][:<type>[<len>]][:<order>][:<count>]

Examples that now parse end-to-end:
  40001                          HoldingRegisters[0], Int16
  400001                         same, 6-digit form
  40001.5                        bit 5 of HR[0]
  40001:F                        Float32 (HR[0..1])
  40001:F:CDAB                   word-swapped Float32
  40001:STR20                    20-char ASCII string
  HR1:DI                         Int32 via mnemonic region
  C100                           Coils[99] (mnemonic)
  40001:F:5                      Float32[5] array (3-field shorthand)
  40001:I:CDAB:10                Int16[10] word-swapped (4-field strict)

Driver-side plumbing:
- ModbusAddressParser + ParsedModbusAddress in the shared Addressing
  assembly. 91 parser tests (every grammar variant + malformed shapes).
- ModbusDataType / ModbusByteOrder moved to shared (with the same namespace
  so callers compile unchanged). ModbusByteOrder gains ByteSwap (BADC) and
  FullReverse (DCBA) alongside the existing BigEndian (ABCD) and WordSwap
  (CDAB).
- NormalizeWordOrder extended to honor all four orders for both 4-byte and
  8-byte values. Old WordSwap behavior preserved bit-for-bit.
- ModbusTagDefinition gains optional ArrayCount.
- ReadOneAsync / WriteOneAsync handle array fan-out: one FC03/04 read covers
  N consecutive register-typed elements, decoded into a typed array (short[],
  float[], etc.). Coil arrays use FC01 reads + FC15 writes (FakeTransport
  in tests gains FC15 support to match).
- DriverAttributeInfo IsArray / ArrayDim flow from ArrayCount so the OPC UA
  address space surfaces ValueRank=1 + ArrayDimensions to clients.
- ModbusDriverFactoryExtensions gains AddressString DTO field. When
  present, the parser drives Region/Address/DataType/ByteOrder/Bit/
  StringLength/ArrayCount; structured fields (Writable, WriteIdempotent,
  StringByteOrder) still come from the DTO. Existing structured tag rows
  keep working unchanged.

Tests: 91 parser unit tests (Driver.Modbus.Addressing.Tests, all green) +
204 driver tests including new ModbusByteOrderTests (BADC/DCBA roundtrips
across Int32/Float32/Float64) and ModbusArrayTests (Int16[5], Float32[3]
CDAB, Coil[10], length-mismatch error, IsArray/ArrayDim discovery).
Solution-wide build clean.

Caveat: grammar names (type codes, byte-order mnemonics, the :count
shorthand) were synthesized from training-era vendor docs. Verify against
current Kepware Modbus Ethernet Driver Help and Ignition Modbus Addressing
manuals before freezing for production deployments — naming may need a
back-compat layer if vendor wording has shifted.

tests/ZB.MOM.WW.OtOpcUa.Driver.Modbus.Tests/ModbusDriverTests.cs

@@ -11,9 +11,11 @@ public sealed class ModbusDriverTests
 {
     /// <summary>
     ///     In-memory Modbus TCP server impl that speaks the function codes the driver uses.
-    ///     Maintains a register/coil bank so Read/Write round-trips work.
+    ///     Maintains a register/coil bank so Read/Write round-trips work. Internal (rather than
+    ///     private) so sibling test files in this project can reuse it without duplicating the
+    ///     fake.
     /// </summary>
-    private sealed class FakeTransport : IModbusTransport
+    internal sealed class FakeTransport : IModbusTransport
     {
         public readonly ushort[] HoldingRegisters = new ushort[256];
         public readonly ushort[] InputRegisters = new ushort[256];
@@ -35,6 +37,7 @@ public sealed class ModbusDriverTests
                 0x04 => Task.FromResult(ReadRegs(pdu, InputRegisters)),
                 0x05 => Task.FromResult(WriteCoil(pdu)),
                 0x06 => Task.FromResult(WriteSingleReg(pdu)),
+                0x0F => Task.FromResult(WriteMultipleCoils(pdu)),
                 0x10 => Task.FromResult(WriteMultipleRegs(pdu)),
                 _ => Task.FromException<byte[]>(new ModbusException(fc, 0x01, $"fc={fc} not supported by fake")),
             };
@@ -92,6 +95,15 @@ public sealed class ModbusDriverTests
             return new byte[] { 0x10, pdu[1], pdu[2], pdu[3], pdu[4] };
         }
 
+        private byte[] WriteMultipleCoils(byte[] pdu)
+        {
+            var addr = (ushort)((pdu[1] << 8) | pdu[2]);
+            var qty = (ushort)((pdu[3] << 8) | pdu[4]);
+            for (var i = 0; i < qty; i++)
+                Coils[addr + i] = ((pdu[6 + (i / 8)] >> (i % 8)) & 0x01) == 1;
+            return new byte[] { 0x0F, pdu[1], pdu[2], pdu[3], pdu[4] };
+        }
+
         public ValueTask DisposeAsync() => ValueTask.CompletedTask;
     }