This PR has no functional changes. Only types are changing and getting
improved (more stricter).
A follow-up PR will come next that does a few functional changes to make
this package fully strict.
actual-server does not need to import the full actual-app/api package.
It can import only the CRDT stuff.. so I'm extracting it into a new
package to reduce the size of actual-server and make the link between
things more transparent.
