canonical paths: check equivalence

[trefis]

For the moment we allow users to annotate module definitions with (** @canonical Some.Path *) but we do not check that Some.Path is indeed equivalent to the module being defined.

[github-actions[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs.

[Julow]

This is still the case.