Try out using msgpack for asset graph

[natebosch]

Towards #41

See if this makes a meaningful difference for performance.

[natebosch]

We typically prefer to avoid taking on a dependency on third party packages from our core tools. We need to decide between accepting a dep, building our own msgpack implementation, or maintaining the use of json...

[jakemac53]

We should also do more investigation into where the slowness is happening here as well - if it is simply the writing of the file to disk we could for instance gzip it.

[mosuem]

Closing this, as it is a few years old now. Feel free to reopen in case you still want to land it!