[lib/keyserver] Improve state sync types

Summary:
ENG-4909

We can keep the very specific types for specs collections that flow gives us, while adding an assert to make sure we don't pass anything that is not a spec to these object. Also replaced * -> any, as they are aliases and * is deprecated.

Test Plan: yarn flow-all

Reviewers: inka, tomek

Reviewed By: tomek

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D9253