Add a callback to the PruneOptions struct which calculates the number of
bytes allowed to be unused after prune is done. This way, the logic is
closer to the option parsing code.
Also, add an explicit option `unlimited` for the use case when storage
does not matter but bandwidth and time do. Internally, this sets the
maximum number of unused bytes to MaxUint64.
Rework the documentation slightly so that no more "packs" are
mentioned and it talks about "files" instead.
Make it clear in the documentation that the percentage given to
`--max-unused` is relative to the whole repository size after pruning is
done. If specified, it must be below 100%, otherwise the repository
would contain 100% of unused data, which is pointless.
I had a hard time coming up with the correct formula to calculate the
maximum number of unused bytes based on the number of used bytes. For a
fraction `p` (0 ≤ p < 1), a repo with `u` bytes used, and the number of
unused bytes `x` the following holds:
x ≤ p * (u+x)
⇔ x ≤ p*u + p*x
⇔ x - p*x ≤ p*u
⇔ x * (1-p) ≤ p*u
⇔ x ≤ p/(1-p) * u
c1a3de4a6e