zmq: read simulator state from the shared TrainState registry

The zmq interface kept its own copy of the state field list, its own name
table and its own packer. All three are now the shared registry, which
resolves the same channel names and returns the same values, so the wire
format is unchanged. New state exposed to external interfaces is added in
one place from now on.

The registry reports the raw velocity rather than zeroing it while the
simulation is paused, and a symbol which doesn't apply to the current
vehicle keeps its measurement and says so through its quality flag.

input/zmq_input.h

@@ -2,45 +2,10 @@
 
 #include <zmq_addon.hpp>
 #include "input/command.h"
+#include "hardware/registry/state_registry.h"
 
 class zmq_input
 {
-    enum class output_fields {
-        shp,
-        alerter,
-        radio_stop,
-        motor_resistors,
-        line_breaker,
-        motor_overload,
-        motor_connectors,
-        wheelslip,
-        converter_overload,
-        converter_off,
-        compressor_overload,
-        ventilator_overload,
-        motor_overload_threshold,
-        train_heating,
-        cab,
-        recorder_braking,
-        recorder_power,
-        alerter_sound,
-        coupled_hv_voltage_relays,
-        velocity,
-        reservoir_pressure,
-        pipe_pressure,
-        brake_pressure,
-        hv_voltage,
-        hv_current_1,
-        hv_current_2,
-        hv_current_3,
-        lv_voltage,
-        distance,
-        radio_channel,
-        springbrake_active,
-        time_month_of_era,
-        time_minute_of_month,
-        time_millisecond_of_day
-    };
 
     zmq::context_t ctx;
     std::optional<zmq::socket_t> sock;
@@ -55,7 +20,8 @@ class zmq_input
 
     struct peer_state {
         float update_interval;
-        std::vector<output_fields> sopi_list;
+        // symbols this peer subscribed to, resolved through the shared TrainState registry
+        std::vector<hardware::state_descriptor const *> sopi_list;
         std::vector<std::tuple<input_type, user_command, user_command, bool>> sipo_list;;
         std::chrono::time_point<std::chrono::high_resolution_clock> last_update;
     };
@@ -64,11 +30,9 @@ class zmq_input
 
     float unpack_float(const zmq::message_t &);
     zmq::message_t pack_float(float f);
-    zmq::message_t pack_field(output_fields f);
 
     std::unordered_map<std::string, user_command> nametocommandmap;
 
-    static std::unordered_map<std::string, output_fields> output_fields_map;
     command_relay relay;
 
 public: