Modify benchmark to only load sources once

Modify benchmark to only load sources once

After a regrettable update,
the benchmark module ended up reloading sources for every compression level.

While the delay itself is likely torelable,
the main issue is that the `--quiet` mode now also displays a loading summary between each compression line.
This wasn't the original intention, which is to produce a compact view of all compressions.

This is fixed in this version,
where sources are loaded only once, for all compression levels,
and loading summary is only displayed once.