Rework LaunchManager-internal LifecycleClient API

[NicolasFussberger]

We currently have lifecycle_client containing the LaunchManager-internal API and lifecycle_client_lib containing the public mw::lifecycle API.

We should rename either one to avoid confusion.

Proposal: Rename the LaunchManager-internal API, as the public API seems already in use.

Naming suggestions:

• LaunchManagerClient
• StateReporter?
• ?

In discussion in the lifecycle call on 08.04.2026 we also decided to expose a public low-level API for reporting the running state (see #148 (comment)).

The LaunchManager-internal API should be reworked to a simple public API and to be moved as part of the mw::lifecycle API.
We shall also provide a mock for the public API.

[NicolasFussberger]

Proposal:
Replace LifecycleClient with the following API.
As an intermediate step, we may keep LifecycleClient and use it to implement below API.
The LifecycleManager should also be adapted to make use of the new API

namespace score
{
namespace mw
{
namespace lifecycle
{

/// @brief Signals to the Launch Manager that this process has finished initialization and is now entering its Running
/// state.
///
/// This function provides an alternative API to the @ref Application class, in which case @ref LifecycleManager
/// internally calls report_running() before invoking the Run() method of the application.
/// Clients may use either report_running() directly or implement the @ref Application class, but not both at the same time.
///
/// @note When using report_running() directly instead of the @ref LifecycleManager class, the caller is responsible for
/// handling process shutdown. The @ref LifecycleManager class automatically registers a signal handler for SIGTERM, which is
/// the signal sent by the Launch Manager to request shutdown of the process. When using report_running() directly,
/// users must register their own SIGTERM signal handler and perform a graceful shutdown accordingly.
void report_running() noexcept;

}
}
}