switch from ST to MT

[drzraf]

Describe the bug
When reloading from ST to MT, I can't reuse the (detached) ArrayBuffer which has been assigned as input data in the ST instance of FFmpeg

To Reproduce

async function makeConfig(mt) {
   return ({
        coreURL: await window.ffmpegUtil.toBlobURL(`${baseURL}/ffmpeg-core.js`, 'text/javascript'),
        wasmURL: await window.ffmpegUtil.toBlobURL(`${baseURL}/ffmpeg-core.wasm`, 'application/wasm'),
        workerURL = mt ? await window.ffmpegUtil.toBlobURL(`${baseURL}/ffmpeg-core.worker.js`, 'text/javascript') : null
   });
}

new FFmpeg();
await ffmpeg.load(await makeConfig(false));
await ffmpeg.writeFile("foo", new Uint8Array(data));
await ffmpeg.exec(['-i', "foo"]);

await ffmpeg.load(await makeConfig(true));
await ffmpeg.writeFile("foo", new Uint8Array(data));  // <-- TypeError: Cannot perform Construct on a detached ArrayBuffer
await ffmpeg.exec(['-i', "foo"]);

Expected behavior
I should be able to switch from ST to MT and reuse the data.

Desktop (please complete the following information):

• OS: Ubuntu
• Browser: Firefox 141 / Chromium 142

Additional context
After using ffprobe I know which codec the video is using. Only then can I choose whether MT is suitable. (For some codecs, like HEVC, it fails and thus must be avoided, but for all others it gives significant performances boost and is desirable)