* Switch to pytest.raises().
* Add matches= to broad pytest.raises().
* Adjust the test_nonserializable_object() regex for Python <= 3.11.
* Adjust the test_nonserializable_object() regex for PyPy.
* Adjust other test exception regexes for PyPy.
* Cleanup.
* tests for other link extractors are moved to test_linkextractors_deprecated.py
* in Python 3 Link is converted to use native strings for urls
* minor cleanups