SlowContactsSystem to SpeedModifierContactsSystem mini rework (#26110)

* rework

* update logic

Content.Shared/Movement/Systems/FrictionContactsSystem.cs

@@ -10,7 +10,7 @@ public sealed class FrictionContactsSystem : EntitySystem
     [Dependency] private readonly SharedPhysicsSystem _physics = default!;
     [Dependency] private readonly MovementSpeedModifierSystem _speedModifierSystem = default!;
 
-    // Comment copied from "original" SlowContactsSystem.cs
+    // Comment copied from "original" SlowContactsSystem.cs (now SpeedModifierContactsSystem.cs)
     // TODO full-game-save 
     // Either these need to be processed before a map is saved, or slowed/slowing entities need to update on init.
     private HashSet<EntityUid> _toUpdate = new();