[Feature Request] Support for Subgraphs/Clusters (i.e. Compound Graphs)

[dolezvo1]

Graphviz has support for so-called compound graphs (formal definition) using the subgraph construct. For example:

digraph G {

  subgraph cluster_0 {
    style=filled;
    color=lightgrey;
    node [style=filled,color=white];
    a0 -> a1 -> a2 -> a3;
    label = "process #1";
  }

  subgraph cluster_1 {
    node [style=filled];
    b0 -> b1 -> b2 -> b3;
    label = "process #2";
    color=blue
  }
  start -> a0;
  start -> b0;
  a1 -> b3;
  b2 -> a3;
  a3 -> a0;
  a3 -> end;
  b3 -> end;

  start [shape=Mdiamond];
  end [shape=Msquare];
}

should render like this:

However, layout-rs currently renders this example (incorrectly) like this (which is, funnily enough, the first image in the project's readme):

[mert-kurttutan]

This feature is implemented in subgraph-sander feature you can check it