Flushes any pending data and metadata operations of the given file stream to disk.

const file = await Deno.open(
  "my_file.txt",
  { read: true, write: true, create: true },
);
await file.write(new TextEncoder().encode("Hello World"));
await file.truncate(1);
await Deno.fsync(file.rid);
console.log(await Deno.readTextFile("my_file.txt")); // H