Add support for named in-memory databases using the ?mode=memory connection query param

[luchsamapparat]

In addition to :memory: SQLite also provides a mode=memory connection query param to instruct SQLite to use a named in-memory database. This is especially useful in combination with cache=shared since it allows the use of distinct in-memory databases within the same process (see SQLite docs.

In my case, I had issues with the in-memory database in my integration tests when using transactions as described in #229). Using cache=shared solved those issues, but introduced another: all tests now shared a common database and weren't isolated anymore. With file:memdb${randomId()}?mode=memory&cache=shared I can create a new in-memory database for each test with a shared cache.

[luchsamapparat]

Hi @penberg! Could you give me feedback if this has any chance of getting merged? (or if there's something I can do to get it merged)