Transpose only a subset of edges when loading graph into Grape

Right now, we transpose the entire graph when loading, so it's compatible with semsim operations.
This isn't quite right as edge types other than is_a don't quite make sense when transposed.

We may need to select only is_a edges when transposing the graph.

Locate the graph-loading code that currently transposes the entire graph, then inspect any existing tests around loading and semsim compatibility. Confirm which edge types are represented and update the behavior so only is_a edges are transposed while other edge types retain their original direction.

Written by the indexing model from the issue text.