plugins: lsps: remove cln dependencies from core module and clean up service

The core module shouldn't depend on anything from the cln_adapters
module. This ensures that we can switch out interfaces in the future
(e.g a different database than cln's datastore).

This change made it necessary to refactor the service plugin which
allowed us to clean it up on the go

Signed-off-by: Peter Neuroth <pet.v.ne@gmail.com>

Author: nepet