Share vertex map with the workers on the same host using shared memory

**Is your feature request related to a problem? Please describe.**
When multiple worker processes are started on the same host (e.g., for auto workers), global vertex maps of fragments will be created multiple times

**Describe the solution you'd like**
Global vertex maps can be placed in shared memory, and getting share across workers on the same host to save the unnecessary memory overhead

**Describe alternatives you've considered**
To support multiple concurrent workers for each process?

The issue names no files, tests, or entry points. Start by locating the global vertex-map and worker-process code in the C++ repository, then determine how same-host workers could share the map. Done means multiple workers on one host reuse shared vertex-map storage without unnecessary duplicate memory.

Written by the indexing model from the issue text.