Intermediate Data Storage Format

Questions:
* How do we want to store data in an intermediate format before moving it to the lm_dataformat that uses json lists?
* Do we even want an intermediate data format?

Let's use this issue to discuss this topic.

Resources:
* https://www.databricks.com/glossary/what-is-parquet#:~:text=What%20is%20Parquet%3F,handle%20complex%20data%20in%20bulk.
* https://arrow.apache.org/