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/Cli/ZB.MOM.WW.OtOpcUa.Driver.Modbus.Cli.Tests/CommandCancellationTests.cs

@@ -19,6 +19,7 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.Modbus.Cli.Tests;
 public sealed class CommandCancellationTests
 {
     /// <summary>Verifies that probe command gracefully handles cancellation during initialization.</summary>
+    /// <returns>A task that represents the asynchronous test.</returns>
     [Fact]
     public async Task ProbeCommand_swallows_cancellation_during_initialize()
     {
@@ -31,6 +32,7 @@ public sealed class CommandCancellationTests
     }
 
     /// <summary>Verifies that read command gracefully handles cancellation during initialization.</summary>
+    /// <returns>A task that represents the asynchronous test.</returns>
     [Fact]
     public async Task ReadCommand_swallows_cancellation_during_initialize()
     {
@@ -49,6 +51,7 @@ public sealed class CommandCancellationTests
     }
 
     /// <summary>Verifies that write command gracefully handles cancellation during initialization.</summary>
+    /// <returns>A task that represents the asynchronous test.</returns>
     [Fact]
     public async Task WriteCommand_swallows_cancellation_during_initialize()
     {

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

@@ -28,6 +28,7 @@ public sealed class ModbusCommandBaseTests
 
         /// <summary>Invokes BuildOptions with the given tags.</summary>
         /// <param name="tags">The list of tag definitions to build options for.</param>
+        /// <returns>The <see cref="ModbusDriverOptions"/> produced by <see cref="ModbusCommandBase.BuildOptions"/>.</returns>
         public ModbusDriverOptions Invoke(IReadOnlyList<ModbusTagDefinition> tags) => BuildOptions(tags);
 
         /// <summary>Invokes ValidateEndpoint.</summary>

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

@@ -21,6 +21,7 @@ public sealed class WriteCommandRegionValidationTests
     /// <param name="region">The read-only Modbus region to attempt a write against.</param>
     /// <param name="type">The data type used in the write attempt.</param>
     /// <param name="value">The raw string value supplied to the write command.</param>
+    /// <returns>A task that represents the asynchronous test operation.</returns>
     [Theory]
     [InlineData(ModbusRegion.DiscreteInputs, ModbusDataType.Bool, "0")]
     [InlineData(ModbusRegion.InputRegisters, ModbusDataType.UInt16, "1")]
@@ -44,6 +45,7 @@ public sealed class WriteCommandRegionValidationTests
 
     /// <summary>Verifies that Coils region requires Bool data type (Driver.Modbus.Cli-002).</summary>
     /// <param name="type">The non-Bool data type that should be rejected for the Coils region.</param>
+    /// <returns>A task that represents the asynchronous test operation.</returns>
     [Theory]
     [InlineData(ModbusDataType.UInt16)]
     [InlineData(ModbusDataType.Int16)]