installation pollutes site-packages with tests

When installing sbws 2.2.0 there are files installed into the following site-packages directories:

• sbsw
• tests
• webclient

tests is definitely not a good location for installation files, they should be below sbsw as well. No sure about the webclient directory.

(Noticed while updating the pkgsrc package.)

In case it matters, Python 3.14.3, setuptools 82.