[lib] refactor state-sync actions in keyserver-reducer to ops

Summary:
Convert logic to ops approach.

Depends on D10761

Test Plan:
Test for fullStateSyncActionType:

1. Make sessionInitializationResult.sessionContinued in keyserver's socket to always return true
2. Make sure updatesCurrentAsOf is properly set after ops

Test for incrementalStateSyncActionType:

1. Close and open app
2. Make sure updatesCurrentAsOf is properly set after ops

Tested on native

Reviewers: inka

Reviewed By: inka

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D10763