docs: complete XML doc comments via fixdocs (2757 to 131 findings)

Add missing <returns>/<param>/<summary>/<typeparam> tags and clean up
misused inheritdoc across 481 files so the documented API surface is
complete. Documentation-only (zero code lines changed). The 131 remaining
findings are inheritdoc-style warnings deliberately left to preserve
hand-written implementation rationale (plan-decision notes, race-condition
explanations).

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Modbus.Tests/ModbusSubscribeOptionsTests.cs

@@ -20,13 +20,9 @@ public sealed class ModbusSubscribeOptionsTests
         public ushort CurrentValue;
         public int WritesSent;
         public int FC06Count;
-        /// <summary>Establishes a connection (no-op for testing).</summary>
-        /// <param name="ct">The cancellation token.</param>
+        /// <inheritdoc />
         public Task ConnectAsync(CancellationToken ct) => Task.CompletedTask;
-        /// <summary>Sends a Modbus PDU and returns a response.</summary>
-        /// <param name="unitId">The Modbus unit ID.</param>
-        /// <param name="pdu">The protocol data unit to send.</param>
-        /// <param name="ct">The cancellation token.</param>
+        /// <inheritdoc />
         public Task<byte[]> SendAsync(byte unitId, byte[] pdu, CancellationToken ct)
         {
             switch (pdu[0])
@@ -52,10 +48,12 @@ public sealed class ModbusSubscribeOptionsTests
             }
         }
         /// <summary>Disposes the transport (no-op for testing).</summary>
+        /// <returns>A completed value task.</returns>
         public ValueTask DisposeAsync() => ValueTask.CompletedTask;
     }
 
     /// <summary>Verifies that deadband filter suppresses changes below the threshold.</summary>
+    /// <returns>A task that represents the asynchronous test operation.</returns>
     [Fact]
     public async Task Deadband_Suppresses_SubThreshold_Changes()
     {
@@ -97,6 +95,7 @@ public sealed class ModbusSubscribeOptionsTests
     }
 
     /// <summary>Verifies that null deadband publishes every value change.</summary>
+    /// <returns>A task that represents the asynchronous test operation.</returns>
     [Fact]
     public async Task Deadband_Null_Publishes_Every_Change()
     {
@@ -122,6 +121,7 @@ public sealed class ModbusSubscribeOptionsTests
     }
 
     /// <summary>Verifies that WriteOnChangeOnly suppresses writes with identical repeated values.</summary>
+    /// <returns>A task that represents the asynchronous test operation.</returns>
     [Fact]
     public async Task WriteOnChangeOnly_Suppresses_Identical_Repeated_Writes()
     {
@@ -141,6 +141,7 @@ public sealed class ModbusSubscribeOptionsTests
     }
 
     /// <summary>Verifies that WriteOnChangeOnly defaults to false and writes all values.</summary>
+    /// <returns>A task that represents the asynchronous test operation.</returns>
     [Fact]
     public async Task WriteOnChangeOnly_Default_False_Always_Writes()
     {
@@ -159,6 +160,7 @@ public sealed class ModbusSubscribeOptionsTests
     }
 
     /// <summary>Verifies that external reads invalidate the WriteOnChangeOnly cache.</summary>
+    /// <returns>A task that represents the asynchronous test operation.</returns>
     [Fact]
     public async Task WriteOnChangeOnly_Cache_Invalidated_By_Read_Divergence()
     {