Do not inherit from Exporter (now requires Exporter 5.57)

Inheriting from Exporter pollutes the namespace while we only need its
'import' sub. Exporter 5.57+ allows to just import that.
'use base ...' => 'use parent ...'

Adds parent.pm as a dependency, but this is a dual life module that is
in perl core since 5.10.1.