fix(pkg-r): querychat_app() should only close connections if it creates the DB

[gadenbuie]

Prior to this PR, if you pass in a database connection to querychat_app() it will close your connection for you. You only would want that if querychat created the table connection internally, i.e. if you passed in a data.frame.

Before

pkgload::load_all()

con <- DBI::dbConnect(duckdb::duckdb())
duckdb::dbWriteTable(con, "mtcars", mtcars)

querychat_app(con, "mtcars")
#> Closing data source...

DBI::dbGetQuery(con, "SELECT * FROM mtcars LIMIT 5;")
#> Error in `dbSendQuery()`:
#> ! Invalid connection
#> ℹ Context: rapi_prepare

After

The database connection remains intact and the dbGetQuery() call completes as expected.

[cpsievert]

Should we do the analogous thing for Python?

[gadenbuie]

Yeah

[gadenbuie]

It turns out Python didn't have a cleanup parameter, so I added that to QueryChat.

Python doesn't have a querychat_app() function, which highlights that this is a special case. I also updated the implementation slightly: we now only clean up if we're given a data.frame that we are turning into a data source. Otherwise, calling $cleanup() destructively ruins a DataSource object, which isn't great.