zig: fix debug crash in uws.Response (#20202)

Author: nektro

src/deps/uws/Response.zig

@@ -10,7 +10,8 @@
 /// - Offers safe casting between Zig and C representations
 /// - Maintains zero-cost abstractions over the underlying µWebSockets API
 pub fn NewResponse(ssl_flag: i32) type {
-    return opaque {
+    // making this opaque crashes Zig 0.14.0 when built in Debug or ReleaseSafe
+    return struct {
         const Response = @This();
         const ssl = ssl_flag == 1;