Refactor world bootstrap and allow empty startup worlds

apps/backend/Universe/Simulation/ITimeService.cs

@@ -0,0 +1,13 @@
+namespace SpaceGame.Api.Universe.Simulation;
+
+public interface ITimeService
+{
+    int TickIntervalMs { get; }
+    TimeSpan TickInterval { get; }
+    float TickDeltaSeconds { get; }
+    double SimulatedSecondsPerRealSecond { get; }
+    DateTimeOffset UtcNow();
+    float ScaleSimulationDelta(float realDeltaSeconds);
+    double ScaleOrbitalDelta(float simulationDeltaSeconds);
+    double CreateInitialOrbitalTimeSeconds(int seed);
+}