`topology` module extrapolation

[HyperCodec]

The topology.rs file is starting to get really long, so it would be good to turn this into a directory module soon to keep it maintainable and readable.

[HyperCodec]

going to close this issue because it's something that I will probably refactor naturally and doesn't require an entire PR

[HyperCodec]

Reopening this because #34 is extrapolating it