(Scanner) Improve error handling for DepWalker

[fraxken]

Current implementation of DepWalker ignore most of the errors happening (sometimes for good reason) but this can hide issues and lead to a complicated debugging experience when a regression occur.

• scanDirOrArchiveEx: catch clause is ignored
• enrichDependency + enrichDependencyVersion: catch clause is ignored

In the beginning we probably need a way to keep and return them in the API.