Composefs --progress-fd bytes_total is broken #2484

Currently, for the ostree backend, we're able to track download progress by dividing bytes by bytes_total. This is useful for showing download progress in plymouth like so.

For composefs, it reports byte information before it even knows what it's downloading, meaning initially it's 0 bytes divided by 0 bytes_total. It also reports bytes separately for each layer being downloaded in parallel.

Composefs and ostree output should have parity with one another.