Support custom allocator for dynamic vamana index

Current SVS [dynamic vamana index](https://github.com/intel/ScalableVectorSearch/blob/f9d40482c2a4d3e82c5452e173a12f88506f54c6/include/svs/index/vamana/dynamic_index.h#L196) does not support custom allocator. The [graph construction ](https://github.com/intel/ScalableVectorSearch/blob/f9d40482c2a4d3e82c5452e173a12f88506f54c6/include/svs/index/vamana/dynamic_index.h#L1202)is by default bound to [HugepageAllocator](https://github.com/intel/ScalableVectorSearch/blob/f9d40482c2a4d3e82c5452e173a12f88506f54c6/include/svs/core/graph/graph.h#L386). It would be beneficial if users could utilize their own allocators for graph construction.