fix: automatic coupler crashes, horns, compressor start delay, radio and cab lever sounds

- automatic couplers don't catch above the safe collision speed (#86): with crash damage on they couple at a
  closing speed of 15 km/h at most, a faster hit locks the coupling until the vehicles part and the collision
  runs its course. On the way: CollisionVelocity() read a head-on 10 + 10 km/h as 14.1 km/h (quaternions turn
  by half the angle), it's now taken from the touching ends; CollisionDetect() took the other vehicle's speed
  the wrong way round for vehicles facing each other. Head-on hits now derail sooner, at the intended limit,
- a single horn lever can't sound both tones at once (eu07/maszyna#392),
- a skid ends once the vehicle stops on locked wheels (eu07/maszyna#479),
- electronic destination signs are blanked at the end of the timetable (eu07/maszyna#446),
- horns need the air or the voltage to sound (eu07/maszyna#290, #76): HornType=[Pneumatic]|Electric and
  Horn3Type in Cntrl.; a pneumatic horn needs 0.2 MPa in the main reservoir (or the main pipe without one),
  an electric one the low voltage; the lever stays where it was put,
- compressor start delay (#67): CompressorStartDelay [s] in Brake., counted from the compressor getting its
  power, after the engine starts say; none by default,
- the channel and volume buttons of a radio without power do nothing (eu07/maszyna#429); the power check of
  the radio is TMoverParameters::RadioPowered(),
- a lever moved smoothly sounds the positions it passes (#83).

Sonar findings in the functions changed: nesting, nested conditionals, commented-out code, std::format,
references to const. Unit tests: test::pair for two vehicles running into each other, test_couplers,
test_horn, test_wheelslip, test_compressor, test_radio, test_gauge_positions.

vehicle/DynObj.cpp

@@ -4825,12 +4825,13 @@ void TDynamicObject::RenderSounds() {
 
     // horns
     {
-        // for moving vehicle combine regular horn activation flag with emergency brake horn activation flag, if the brake is active
-        auto const warningsignal { (
-            MoverParameters->Vel > 0.5 && MoverParameters->AlarmChainFlag ?
+        // for moving vehicle combine regular horn activation flag with emergency brake horn activation flag, if the brake is active;
+        // the horns without the air or the voltage they need stay silent
+        auto const warningsignal { MoverParameters->SoundingHorns(
+            ( MoverParameters->Vel > 0.5 && MoverParameters->AlarmChainFlag ?
                 MoverParameters->EmergencyBrakeWarningSignal :
                 0 )
-            | MoverParameters->WarningSignal };
+            | MoverParameters->WarningSignal ) };
 
         if( TestFlag( warningsignal, 1 ) ) {
             sHorn1.play( sound_flags::exclusive | sound_flags::looping );
@@ -7794,7 +7795,14 @@ int TDynamicObject::RouteWish(TTrack *tr)
     return Mechanik ? Mechanik->CrossRoute(tr) : 0; // wg AI albo prosto
 };
 
-void TDynamicObject::DestinationSet(std::string to, std::string numer) {
+void TDynamicObject::DestinationClear() {
+
+    if( false == DestinationSign.has_light ) { return; } // physical destination signs remain up until manually changed
+    // update_destinations() shows the blank sign in place of the missing destination
+    DestinationSign.destination = null_handle;
+}
+
+void TDynamicObject::DestinationSet(std::string const &to, std::string const &numer) {
     // ustawienie stacji docelowej oraz wymiennej tekstury 4, jeśli istnieje plik
     // w zasadzie, to każdy wagon mógłby mieć inną stację docelową
     // zwłaszcza w towarowych, pod kątem zautomatyzowania maewrów albo pracy górki
@@ -7823,6 +7831,15 @@ void TDynamicObject::DestinationSet(std::string to, std::string numer) {
     if( DestinationSign.script.empty() ) { return; } // no script so no way to make the texture
     if( numer == "none" )                { return; } // blank or incomplete/malformed timetable, don't bother
 
+    auto const trainname { [this]() -> std::string {
+        if( ctOwner != nullptr ) { return ctOwner->TrainName(); }
+        if( Mechanik != nullptr ) { return Mechanik->TrainName(); }
+        return "none"; } }; // shouldn't get here but, eh
+    auto const instance { [this]() -> std::string {
+        if( DestinationSign.instancing == "name" ) { return MoverParameters->Name; }
+        if( DestinationSign.instancing == "type" ) { return MoverParameters->TypeName; }
+        return "none"; } };
+
     std::string signrequest {
           "make:"
         + DestinationSign.script
@@ -7834,17 +7851,10 @@ void TDynamicObject::DestinationSet(std::string to, std::string numer) {
                 ctOwner->Vehicle()->MoverParameters->Name ) // owned vehicle, safer to point to owner as carriages can have identical names
         // basic instancing string
         // NOTE: underscore doesn't have any magic meaning for the time being, it's just less likely to conflict with regular dictionary keys
-        + "&_id1=" + (
-            ctOwner != nullptr ? ctOwner->TrainName() :
-            Mechanik != nullptr ? Mechanik->TrainName() :
-            "none" ) }; // shouldn't get here but, eh
+        + "&_id1=" + trainname() };
     // TBD, TODO: replace instancing with support for variables in extra parameters string?
     if( false == DestinationSign.instancing.empty() ) {
-        signrequest +=
-            "&_id2=" + (
-                DestinationSign.instancing == "name" ? MoverParameters->Name :
-                DestinationSign.instancing == "type" ? MoverParameters->TypeName :
-                "none" );
+        signrequest += "&_id2=" + instance();
     }
     // optionl extra parameters
     if( false == DestinationSign.parameters.empty() ) {