Include testing for DuckDb results databases #83
Description
There is currently no reason why DuckDb cannot be supported by this package and results models. It is also an appealing platform for testing and usage as the SQL syntax is largely equivalent to postgres. However, this has not been tested in this package and some functionality here may fail.
For this reason, tests around the support of DuckDb should be examined.
There are also appealing features DuckDb supports that may be of use, for example, attaching to postgres databases within the connection which can allow joining or transferring data to a remote database. This could be very useful in the case of local results that may wish to query against, for example, a hosted vocabulary schema without requiring the user to download anything. This would be useful in the case of shiny apps. CohortDiagnostics currently requires an export of concepts and concept ancestory/relationships which consumes a large amount of space. Supporting a hosted vocabulary would significantly reduce the result export size. Similarly, shared Achilles data counts could be used within projects.