FaissKnnVectorsFormat byte vectors support

now FaissKnnVectorsFormat doesn’t support KnnByteVectorField. Because of this, a few tests in TestFaissKnnVectorsFormat are currently disabled.

Faiss only works with float32 vectors. It doesn’t have a native byte vector type like Lucene does.

Start with FaissKnnVectorsFormat and the disabled tests in TestFaissKnnVectorsFormat. Read the existing float32-vector handling and inspect what the disabled KnnByteVectorField cases expect, keeping in mind that Faiss has no native byte vector type. Done means byte-vector support is implemented and the relevant tests can be enabled and pass.

Written by the indexing model from the issue text.