Uses duckdb::duckdb() as backend. nodbi creates or
uses a DuckDB table, with columns _id and json created and used
by package nodbi, applying SQL functions as per
https://duckdb.org/docs/extensions/json to the json column.
Each row in the table represents a JSON document.
Any root-level _id is extracted from the document(s) and used for
column _id, otherwise a UUID is created as _id.
The table is indexed on _id.
For a benchmark, see https://github.com/ropensci/nodbi#benchmark.