[BUG] CAGRA IP Distance returning invalid neighbors

[cjnolet]

Zilliz changed their CAGRA testing for IP distance to generate random numbers with negatives and they found some of the neighbors being returned are -1.

What's also weird about their test results is that they were using nn-descent and not getting an exception (since nn-descent doesn't yet support IP).

While beginning triage this issue in Python, I realized that the IP distance was never exposed in the Python layer. We should fix this and also add explicit pytests to verify 1) correct neighbors are returned when negatives are in the input vectors, and 2) the algorithm fails gracefully when IP distance is used with nn-descent as the build algo.

[cjnolet]

Attaching dataset / reproducer provided by Zilliz: https://github.com/zilliztech/knowhere/blob/5ac21caffcb733963b531d1ceb02eb4400365144/test_b.cc#L15