Mock query execution strategies for tests marked with "remote"

[lu-pl]

Some higher level tests target an actual remote triplestore. Obviously, those cases should be mocked instead.

Mocking HttpxStrategy shouldn't be a problem, mocking SPARQLWrapper and the respective rdfproxy strategy is not entirely straight forward though. I opened a SPARQLWrapper issue with a mock solution, no response so far.

So, since the SPARQLWrapperStrategy can be considered deprecated anyway, I would only mock HttpxStrategy and then discontinue SPARQLWrapper for RDFProxy.