Add comment about thread safety

Author: marianotepper

jvector-base/src/main/java/io/github/jbellis/jvector/graph/similarity/BuildScoreProvider.java

@@ -138,6 +138,7 @@ public SearchScoreProvider diversityProviderFor(int node1) {
      * with reranking performed using RandomAccessVectorValues (which is intended to be
      * InlineVectorValues for building incrementally, but should technically
      * work with any RAVV implementation).
+     * This class is not thread safe, we should never its results to another thread.
      */
     static BuildScoreProvider pqBuildScoreProvider(VectorSimilarityFunction vsf, PQVectors pqv) {
         int dimension = pqv.getOriginalSize() / Float.BYTES;