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.Browser.Tests/OpcUaClientDriverBrowserTests.cs

@@ -19,6 +19,7 @@ public sealed class OpcUaClientDriverBrowserTests
     public void DriverType_is_OpcUaClient() => _sut.DriverType.ShouldBe("OpcUaClient");
 
     /// <summary>An empty endpoint must fail fast with a clear EndpointUrl-mentioning message.</summary>
+    /// <returns>A task that represents the asynchronous test operation.</returns>
     [Fact]
     public async Task OpenAsync_with_empty_endpoint_throws()
     {
@@ -29,6 +30,7 @@ public sealed class OpcUaClientDriverBrowserTests
     }
 
     /// <summary>A JSON literal that deserializes to null must fail fast.</summary>
+    /// <returns>A task that represents the asynchronous test operation.</returns>
     [Fact]
     public async Task OpenAsync_with_null_json_throws()
     {
@@ -41,6 +43,7 @@ public sealed class OpcUaClientDriverBrowserTests
     /// must say so explicitly rather than surfacing a downstream COM/SDK error.
     /// <c>OpcUaAuthType.Certificate</c> serializes as the numeric value 2 under the
     /// browser's default System.Text.Json options (no string-enum converter).</summary>
+    /// <returns>A task that represents the asynchronous test operation.</returns>
     [Fact]
     public async Task OpenAsync_with_certificate_auth_throws_clear_message()
     {