Add AbstractGraphIndexWriter::getDimension

Author: michaeljmarshall

jvector-base/src/main/java/io/github/jbellis/jvector/graph/disk/AbstractGraphIndexWriter.java

@@ -82,6 +82,10 @@ public Set<FeatureId> getFeatureSet() {
         return featureMap.keySet();
     }
 
+    public int getDimension() {
+        return dimension;
+    }
+
     long featureOffsetForOrdinal(long startOffset, int ordinal) {
         int edgeSize = Integer.BYTES * (1 + graph.getDegree(0));
         long inlineBytes = ordinal * (long) (Integer.BYTES + inlineFeatures.stream().mapToInt(Feature::featureSize).sum() + edgeSize);