Dynamic linking of Caqti drivers using findlib.dynload.

This library registers a dynamic linker which will be called when encoutering an unhandled database URI. It tries to load a findlib package named "caqti-driver-<scheme>" where "<scheme>" is the scheme of the URI, which is expected register a driver for the scheme.

This is a separate package to avoid the dependency on the findlib.dynload for architectures, like MirageOS, where dynamic linking may be unavailable. The alternative is to link drivers directly into the application.