The directory created by `T.TempDir` is automatically removed when the
test and all its subtests complete.
Reference: https://pkg.go.dev/testing#T.TempDir
Signed-off-by: Eng Zer Jun <engzerjun@gmail.com>
This allows lots of behaviour to be baked into the new Client, Torrent and Piece wrappers, rather than duplicating (badly) them in all the backend implementations.