Fix caching issue with Transformers.js workloads in incognito mode

[danleh]

There is still some caching issue with transformers.js, but which appears only in incognito/private browsing mode (which is relevant, since some benchmark guides recommend/runners use a fresh profile or incognito mode to get somewhat reliable "cold start" measurements). You can confirm that by running in incognito mode and checking the DevTools -> Network tab, where the model weights and wasm file will be requested N times, see screenshot: