refactor(Encryption): Migrate to strong types

[provokateurin]

Summary

I noticed that if (!$this->storage->file_exists($this->internalPath)) { was called with null as $internalPath which is not allowed.
Added strong types and fixed the tests which were giving wrong/incomplete inputs.

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)

[provokateurin]

Wrapper\Encryption has similar troubles, gonna fix that as well.