Simplify usage and installation

[sudara]

This PR

1. Simplifies installation by removing the singleton
2. Bumps the google dependency to version 50.1

New usage:

#if PERFETTO
    MelatoninPerfetto tracingSession;
#endif

If you prefer to manually start the session, you can do so by passing false to the constructor and manually calling .beginSession and .endSession.

Old usage:

#if PERFETTO
    std::unique_ptr<perfetto::TracingSession> tracingSession;
#endif

#if PERFETTO
    MelatoninPerfetto::get().beginSession();
#endif

#if PERFETTO
    MelatoninPerfetto::get().endSession();
#endif