Cleanup the import logic and improve errors

[fsimonis]

This PR cleans up the import logic and improves import error message.

• The import_module function was used incorrectly. This is now fixed. I am still unsure why it works when passing a file with a .py suffix as it expects a module.
• The import module step is now a separate step and errors are split into 3 groups:
  • The configured module cannot be found
  • The configured module has dependencies that cannot be found
  • Something else went wrong
• Then the class is detected with a potential suffix of 0-9
• Finally the class is wrapped

Checklist:

• I made sure that the CI passed before I ask for a review.
• I added a summary of the changes (compared to the last release) in the CHANGELOG.md.
• If necessary, I made changes to the documentation and/or added new content.
• I will remember to squash-and-merge, providing a useful summary of the changes of this PR.