Refactor FTL time tracking code to fix a UI bug (#26538)

The FTL UI on the shuttle console would reset the FTL progress bar every time you open it. This is because the server only sends "time until completion", not a start/end time. The FTL code now uses a separate start/end time so the exact same progress bar can be preserved.

For convenience, I made a StartEndTime record struct that stores the actual tuple. This is now used by the code and has some helpers.

Content.Server/Shuttles/Systems/ShuttleSystem.cs

@@ -19,6 +19,7 @@ using Robust.Shared.Physics;
 using Robust.Shared.Physics.Components;
 using Robust.Shared.Physics.Systems;
 using Robust.Shared.Random;
+using Robust.Shared.Timing;
 
 namespace Content.Server.Shuttles.Systems;
 
@@ -30,6 +31,7 @@ public sealed partial class ShuttleSystem : SharedShuttleSystem
     [Dependency] private readonly IMapManager _mapManager = default!;
     [Dependency] private readonly IRobustRandom _random = default!;
     [Dependency] private readonly ITileDefinitionManager _tileDefManager = default!;
+    [Dependency] private readonly IGameTiming _gameTiming = default!;
     [Dependency] private readonly BiomeSystem _biomes = default!;
     [Dependency] private readonly BodySystem _bobby = default!;
     [Dependency] private readonly DockingSystem _dockSystem = default!;
@@ -68,7 +70,7 @@ public sealed partial class ShuttleSystem : SharedShuttleSystem
     public override void Update(float frameTime)
     {
         base.Update(frameTime);
-        UpdateHyperspace(frameTime);
+        UpdateHyperspace();
     }
 
     private void OnGridFixtureChange(EntityUid uid, FixturesComponent manager, GridFixtureChangeEvent args)