fix: use byte-length for close message truncation, add exception-safe disposal

- CreateCloseMessage now operates on UTF-8 byte length (matching Go's
  len(body) behavior) instead of character length, with proper UTF-8
  boundary detection during truncation
- WsCompression.Compress now uses try/finally for exception-safe disposal
  of DeflateStream and MemoryStream

src/NATS.Server/WebSocket/WsCompression.cs

@@ -22,19 +22,24 @@ public static class WsCompression
     {
         var output = new MemoryStream();
         var deflate = new DeflateStream(output, CompressionLevel.Fastest, leaveOpen: true);
-        deflate.Write(data);
-        deflate.Flush();
+        try
+        {
+            deflate.Write(data);
+            deflate.Flush();
 
-        var compressed = output.ToArray();
+            var compressed = output.ToArray();
 
-        deflate.Dispose();
-        output.Dispose();
+            // Remove trailing 4-byte sync marker (0x00 0x00 0xff 0xff) per RFC 7692
+            if (compressed.Length >= 4)
+                return compressed[..^4];
 
-        // Remove trailing 4-byte sync marker (0x00 0x00 0xff 0xff) per RFC 7692
-        if (compressed.Length >= 4)
-            return compressed[..^4];
-
-        return compressed;
+            return compressed;
+        }
+        finally
+        {
+            deflate.Dispose();
+            output.Dispose();
+        }
     }
 
     /// <summary>