mypy cache folder causes generated requirements to be empty

Related to #73.

Steps to reproduce

Create foo.py:
```
import requests
```

Run the following commands:


$ pipreqs --print
requests==2.28.1
INFO: Successfully output requirements

$ mypy foo.py Success: no issues found in 1 source file

$ pipreqs --print

INFO: Successfully output requirements


I would expect 'requests' to still be in the generated requirements after running mypy.
### Description
Since mypy creates a subfolder called `.mypy_cache/3.10/requests`, pipreqs will add it to 'candidates' which causes the import to be satisfied, even though foo.py is obviously not going to attempt to import that folder. Ignoring `.mypy_cache` is the simple fix, but maybe folders shouldn't be considered packages unless they contain an `__init__.py`?
https://github.com/bndr/pipreqs/blob/a593d27e3d9fcdecc0fbf385ef43116cccad71ec/pipreqs/pipreqs.py#L104-L108
https://github.com/bndr/pipreqs/blob/a593d27e3d9fcdecc0fbf385ef43116cccad71ec/pipreqs/pipreqs.py#L143-L144

bndr / pipreqs

mypy cache folder causes generated requirements to be empty #330

Steps to reproduce