client/dotnet: backfill XML doc comments to satisfy analyzers

Adds missing <summary>/<param> docs across the .NET client library and its
test suite so CommentChecker reports zero issues. TreatWarningsAsErrors
requires the analyzer surface clean before publishing the NuGet package.

clients/dotnet/ZB.MOM.WW.MxGateway.Client/MxGatewayClientOptions.cs

@@ -47,6 +47,9 @@ public sealed class MxGatewayClientOptions
     /// </summary>
     public TimeSpan? StreamTimeout { get; init; }
 
+    /// <summary>
+    /// Gets the maximum size in bytes for gRPC messages.
+    /// </summary>
     public int MaxGrpcMessageBytes { get; init; } = 16 * 1024 * 1024;
 
     /// <summary>