simulate package count and size

After running things like apk add/del/upgrade there is a summary of installed packages and the current size.

When simulating the installation the reals size and count is used instead of simulating it:

~ $ apk -s add sudo
...
OK: 6652 MiB in 1435 packages
~ $ doas apk add sudo
...
OK: 6654 MiB in 1437 packages

I assume this could be fixed in src/commit.c#apk_solver_commit_changeset. The variable size_diff could be used to simulate the size correctly and the changeset for the amount of packages.

The verbose version also writes the files and dirs. I don't know if they can be simulated easily but if they can that would be nice too.