* Moved `source.Files` to its own package, thus the type is now `files.Files`.
* Moved much of the location functionality from pkg `source` to its own package `location`.
* go1.21: changes to support slog as part of stdlib
* Removed accidentially checked-in line of code
* Fixed minor linting issues; reenable typecheck
* go1.21: switched to stdlib slices pkg