fix: recursively run tests for dir

[fredrikaverpil]

Why this change?

The current implementation did not take into account:

• Recursively run tests for given package (in sub-packages).
• If no exact correlation was found between folder path and package import path, a search for sub-packages is conducted. The result can be used for inferring a proper package import path.

Huge thanks to @damoye for uncovering this rather large bug! ❤️

What was done?

• Introduce two search strategies for correlating the selected folderpath with a package import path.
• Append /... at the end of the package import path.

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fixes: #228