Add rerank field to VecSimDiskContext for disk-based HNSW

MOD-13179: Add boolean rerank field to VecSimDiskContext struct to support
the RERANK parameter for disk-based HNSW indexes. This parameter controls
whether reranking is enabled during search operations.

Author: ofiryanai

src/VecSim/vec_sim_common.h

@@ -250,6 +250,7 @@ typedef struct {
     void *storage; // Opaque pointer to disk storage
     const char *indexName;
     size_t indexNameLen;
+    bool rerank; // Whether to enable reranking for disk-based HNSW
 } VecSimDiskContext;
 
 typedef struct {