OK you explicitly asked about the "package" not the "file". But that's not how it works because the same package can be present in different files. (think of main:: for instance)

Assuming the normal case that the package scope is only in one single file...

If this is only a one-time application, finding the correct file-path shouldn't be a problem.

Otherwise one could write an alias which finds the filename for a provided package and sets the breakpoint.

Compare also %INC which lists the filenames for used modules.