🚧 WIP: Replace default python json library with orjson

[ff137]

json operations are notoriously expensive, especially with the default python library. orjson boasts 10x fastert de/serialisation speeds. So it'd be great if the python wrapper offered orjson an optional alternative.

Adding orjson as an optional dependency will be more manageable with poetry #302

[andrewwhitehead]

Superseded by #327, although updating to use poetry and adding orjson as an optional dependency would still be nice.