[BUG] NPE with Faiss Byte Vectors when filtering

[naveentatikonda]

What is the bug?
Running into NullPointerException when we are computing P * Dimension <= Max_distance_computations for faiss efficient filters using byte vectors. But, it is working fine for all other scenarios.

{
  "error": {
    "root_cause": [
      {
        "type": "null_pointer_exception",
        "reason": "Cannot read the array length because the return value of \"org.opensearch.knn.index.query.KNNQuery.getByteQueryVector()\" is null"
      }
    ],
    "type": "search_phase_execution_exception",
    "reason": "all shards failed",
    "phase": "query",
    "grouped": true,
    "failed_shards": [
      {
        "shard": 0,
        "index": "development-20241204111110-3de6471c",
        "node": "5ry1X70gTgyIOlMItg6TzA",
        "reason": {
          "type": "null_pointer_exception",
          "reason": "Cannot read the array length because the return value of \"org.opensearch.knn.index.query.KNNQuery.getByteQueryVector()\" is null"
        }
      }
    ],
    "caused_by": {
      "type": "null_pointer_exception",
      "reason": "Cannot read the array length because the return value of \"org.opensearch.knn.index.query.KNNQuery.getByteQueryVector()\" is null",
      "caused_by": {
        "type": "null_pointer_exception",
        "reason": "Cannot read the array length because the return value of \"org.opensearch.knn.index.query.KNNQuery.getByteQueryVector()\" is null"
      }
    }
  },
  "status": 500
}

Proposed Solution
Here, we are trying to get byteQueryVector instead of queryVector. We need to get queryVector here because for byte datatype with Faiss engine we will do byte range validation and still store it as a normal query vector to pass it later to Faiss ScalarQuantizer. The Faiss SQ expects the query vector as an fp32 vector.

The fix with integ test in my feature branch - naveentatikonda@bbeb3de