test: SonarCloud issues of the unit tests

- test::definition_error for unusable test vehicle definitions instead of
  std::runtime_error (S112)
- the rows of a table section written by a function of their own, less
  nesting in definition::text() (S134)
- std::less<> for the section table (S6045)
- comments in the empty methods of the reseeding listener and stub (S1186)
- NOSONAR where the engine's headers fix the stubs: the extern globals
  and the member function signatures (S5421, S5817, S1238)
- NOSONAR on LoadFIZ_Parse(): the cognitive complexity is the former body
  of LoadFIZ(), moved as it was (S3776)
- a comment Sonar took for code reworded (S125)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/unit/vehicle.h

@@ -1,6 +1,7 @@
 #pragma once
 
 #include <memory>
+#include <stdexcept>
 #include <string>
 
 #include <nlohmann/json.hpp>
@@ -9,6 +10,12 @@
 
 namespace test {
 
+// thrown for a test vehicle definition which can't be used: missing, malformed, or not taken by the loader
+class definition_error : public std::runtime_error {
+public:
+	using std::runtime_error::runtime_error;
+};
+
 // definition of a test vehicle: one of the JSON files in tests/unit/data, with the sections and keys
 // of the game's vehicle definitions, changed by the test where it needs to:
 //   auto heavy = definition::load("wagon").set("Param", "M", 60000).set("Brake", "BrakeValve", "ESt3");
@@ -53,7 +60,7 @@ public:
 	// advances the physics by Seconds in steps of Dt
 	void run(double Seconds, track const &Track = {}, double Dt = 0.01);
 
-	// vehicle speed [km/h], signed
+	// vehicle speed in kilometres per hour, negative when moving backwards
 	double speed() const { return m_mover->V * 3.6; }
 
 private: