Progress Metrics Calculation Engine

As a user, I want to see the precise progress (percentage, remaining files) of each active job, So that I can easily estimate the remaining time for my backups.

Given a backup job with a total of 100 files,
When 25 files are successfully copied,
Then the calculated progress percentage is exactly 25%.

Given an active backup job,
When a single file finishes transferring,
Then the "Size of remaining files" and "Number of remaining files" are correctly decremented in the state data.