Add performance metrics for queries, transformations, etc.

[kesmit13]

It would be nice to have a way to retrieve performance metrics to determine where most of the time is being spent in an API call. The calls mainly consist of making a query, downloading the result, transforming the data, and returning the final data structure. Being able to see immediately how much time is being spent during each phase would give a lot of insights into performance issues. This will be especially helpful when using the Ibis SingleStoreDB backend which does lazy evaluation. It can be easy to accidentally trigger a download of large amounts of data (possibly multiple times), and having metrics readily available would help diagnose that.