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/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer.Tests/SdkServiceLevelPublisherTests.cs

@@ -20,6 +20,7 @@ public sealed class SdkServiceLevelPublisherTests : IDisposable
         $"otopcua-pki-{Guid.NewGuid():N}");
 
     /// <summary>Verifies that the publisher writes values to the standard Server.ServiceLevel variable.</summary>
+    /// <returns>A task that represents the asynchronous test operation.</returns>
     [Fact]
     public async Task Publish_writes_value_to_Server_ServiceLevel_variable()
     {
@@ -49,6 +50,7 @@ public sealed class SdkServiceLevelPublisherTests : IDisposable
     }
 
     /// <summary>Verifies that publishing service level values is idempotent when called multiple times.</summary>
+    /// <returns>A task that represents the asynchronous test operation.</returns>
     [Fact]
     public async Task Publish_is_idempotent_when_called_multiple_times()
     {