Set a minimum pin for `apsw`

The requirements in `settings.ini` are currently set to `requirements = fastcore apsw`, but this package imports submodules (apsw.ext, apsw.bestpractice) that were introduced around `apsw v3.43`. Adding a minimum version pin would ensure that both pip and conda install a compatible version.

Open settings.ini and inspect the requirements entry for fastcore and apsw. Add a minimum apsw version around v3.43 so the apsw.ext and apsw.bestpractice imports are supported, then verify that the dependency specification is suitable for both pip and conda installation.

Written by the indexing model from the issue text.