feat(build): update checksums when editing source files during build

Using the --edit option while doing a build frequently implies making changes to the sources...whether it is updating a URL or dropping obsolete patches or other changes. It isn't a 100% correlation of course, but more often than not any changes made during editing are expected to also update the checksums to be in sync.

Using the --pkgver option already triggers this, but other subsequent edits do not making for frequent failed edit/build cycles.