Improvement: Rework ProcessStateClient API to be an internal API

[eelcoem]

Currently, the ProcessStateClient is an API that uses shared memory for communication (to communicate process states btw. LM daemon and HM daemon).

After #9 the LaunchManager (LM) and HealthMonitor (HM) are integrated as a single daemon.
Therefore, shared memory communication is no longer required and we can simplify this interface.

Tasks:

• Rework the ProcessStateClient interface to not use shared memory
• Preferably, introduce a C++ interface and make use of dependency injection on both sides: LM and HM for better testability