Add tools to support query optimization

[tylerwilding-wk]

It would be great if there was a way to inspect the shape of data and its relationships in eva (to help guide how the query should be written to traverse efficiently) or a way to inspect the stages between each query clause (i.e., a way to see we're using a very general clause first, filtering almost nothing and causing poor performance). Essentially: anything to help guide query optimization."

Essentially something similar to https://github.com/dwhjames/datomic-q-explain
Another useful tool might be to show the query and inputs for slow-running queries.