Make Runner:run() more verbose in case of failure

[ocean90]

Issue Overview

❯ wp @translate traduttore project update 239
Warning: Could not update translations for project (ID: 239)!

It would be nice to display why exactly the translations could not be updated. The command uses Runner:run() which unfortunately only returns "True on success, false otherwise.".
In my case it was a stale lock so I was expecting that the warning would mention that.

I think Runner:run() should be updated to return a WP_Error object or throw an exception in case of failures.

[swissspidy]

It's also impossible to tell whether the update failed at the POT generation or at the import stage in Updater::update().

Throwing exceptions throughout the codebase for failures like this, which could then be caught in ProjectCommand or earlier, would make this easier for sure.