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.OpcUaClient.Tests/OpcUaClientDriverScaffoldTests.cs

@@ -45,6 +45,7 @@ public sealed class OpcUaClientDriverScaffoldTests
     }
 
     /// <summary>Verifies that Initialize against unreachable endpoint transitions to Faulted and throws.</summary>
+    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task Initialize_against_unreachable_endpoint_transitions_to_Faulted_and_throws()
     {
@@ -72,6 +73,7 @@ public sealed class OpcUaClientDriverScaffoldTests
     }
 
     /// <summary>Verifies that Reinitialize against unreachable endpoint re-throws the error.</summary>
+    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task Reinitialize_against_unreachable_endpoint_re_throws()
     {