fix(modbus): review r0 - FC23 opt-in, explicit maxReadGap 0 = off, legacy coil types load, one health writer

Coordinator rulings and Important findings from review r0:
1. FC23 is opt-in (new UseFC23ForMultiRegisterWrites, default false); a config
   without it - including the persisted "disableFC23": false every form-saved
   config carries - keeps the FC16 wire. DisableFC23 stays the hard kill-switch.
2. An explicit maxReadGap 0 means coalescing off again (its pre-lane meaning);
   the gap-8 default applies only to an absent key.
3. Coils/DiscreteInputs tags persisted with a register dataType (the old
   editor saved Int16) are coerced to Bool, never refused, with no deploy
   warning (a warning can be promoted to a blocking error). The editor loads
   them as Bool. Register region + Bool is still refused.
4. One comms-fault slot for reads and writes: a good read clears a write's
   transport fault and vice versa.
Minors: Dispose writes its own Unknown health (m1); persisted region/address
are authoritative over addressString so a Family change cannot remap a live
tag (m2); a malformed-but-delivered reply no longer fails the unit fast (m3);
a fresh socket published after a concurrent dispose is torn down (m4); the
editor resets address text per tag (m5); master merged (m6); the FC23 latch
log says re-init restores it (m7). Back-compat tests use the old persisted
JSON shapes and fail without the fixes.

Refs #741
Claude-Session: https://claude.ai/code/session_01Ub9hGmYLQvn9XETzw7CMsT

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

@@ -85,6 +85,7 @@ public static class ModbusDriverFactoryExtensions
             UseFC15ForSingleCoilWrites = dto.UseFC15ForSingleCoilWrites ?? false,
             UseFC16ForSingleRegisterWrites = dto.UseFC16ForSingleRegisterWrites ?? false,
             DisableFC23 = dto.DisableFC23 ?? false,
+            UseFC23ForMultiRegisterWrites = dto.UseFC23ForMultiRegisterWrites ?? false,
             WriteOnChangeOnly = dto.WriteOnChangeOnly ?? false,
             MaxReadGap = dto.MaxReadGap ?? ModbusDriverOptions.DefaultMaxReadGap,
             DisableReadCoalescing = dto.DisableReadCoalescing ?? false,
@@ -187,6 +188,8 @@ public static class ModbusDriverFactoryExtensions
         public bool? UseFC16ForSingleRegisterWrites { get; init; }
         /// <summary>Gets or sets a value indicating whether to disable function code 23.</summary>
         public bool? DisableFC23 { get; init; }
+        /// <summary>Gets or sets a value indicating whether multi-register writes opt in to FC23 write + read-back.</summary>
+        public bool? UseFC23ForMultiRegisterWrites { get; init; }
         /// <summary>Gets or sets a value indicating whether to write only on change.</summary>
         public bool? WriteOnChangeOnly { get; init; }
         /// <summary>Gets or sets the maximum gap between register addresses for coalescing.</summary>