Return n_lost_pulses in sync from receiver

In order to have proper statistics we need to return the
number of lost pulses from the receiver. We cannot just count
the gap in pulse_id as the beam might be operated at
different frequencies.

sf-stream/include/ZmqPulseSyncReceiver.hpp

@@ -8,6 +8,11 @@
 
 #include "formats.hpp"
 
+struct PulseAndSync {
+    const uint64_t pulse_id;
+    const uint32_t n_lost_pulses;
+};
+
 class ZmqPulseSyncReceiver {
 
     void* ctx_;
@@ -22,7 +27,7 @@ public:
             const int n_modules);
     ~ZmqPulseSyncReceiver();
 
-    uint64_t get_next_pulse_id() const;
+    PulseAndSync get_next_pulse_id() const;
 };