feat(c++): use nested namespace to distinguish different level reader/writer

[acezen]

Describe the enhancement requested

Currently GraphAr c++ library use the class name to distinguish different level reader/writer like VertexPropertyChunkInfoReader as info level vertex property reader and VertexPropertyArrowChunkReader as arrow vertex property reader. This makes the name too long and not concise.

Maybe we can use nested namespace to replace the naming like: VertexPropertyChunkInfoReader -> graphar::VertexChunkReader VertexPropertyArrowChunkReader -> graphar::arrow::VertexChunkReader AdjListChunkInfoReader -> graphar:AdjListChunkReader AdjListArrowChunkReader -> graphar::arrow::AdjListChunkReader AdjListOffsetChunkInfoReader -> graphar::OffsetChunkReader AdjListPropertyChunkInfoReader -> graphar::EdgePropertyChunkReader AdjListOffsetArrowChunkReader -> graphar::arrow::OffsetChunkReader AdjListPropertyArrowChunkReader -> graphar::arrow::EdgePropertyChunkReader

VertexChunkInfoWriter -> graphar::VertexChunkWriter VertexChunkArrowWriter -> graphar::arrow::VertexChunkWriter EdgeChunkInfoWriter -> graphar::EdgeChunkWriter EdgeChunkArrowWriter -> graphar::arrow::EdgeChunkWriter

Component(s)

C++