Improve rustup updates performance by starting with a parallel check #4747
Description
As discussed here, the performance of rustup update could be improved compared to rustup check.
When no updates are available, rustup update is about 3x slower than rustup check.
This happens because the channels are checked sequentially for updates, while rustup check performs these checks concurrently.
A possible improvement would be to perform a parallel check before starting the update process itself; allowing the performance of a no-op rustup update to match that of rustup check.