Add Galoshes slowdown over slippery surfaces (#30967)

* first draft

* Fixed it all, just need to rename stuff

* Rename and add comments

* Clean-up

* Access added

Content.Shared/Movement/Events/GetSpeedModifierContactCapEvent.cs

@@ -0,0 +1,22 @@
+using Content.Shared.Inventory;
+
+namespace Content.Shared.Movement.Events;
+
+/// <summary>
+/// Raised on an entity to check if it has a max contact slowdown.
+/// </summary>
+[ByRefEvent]
+public record struct GetSpeedModifierContactCapEvent() : IInventoryRelayEvent
+{
+    SlotFlags IInventoryRelayEvent.TargetSlots => ~SlotFlags.POCKET;
+
+    public float MaxSprintSlowdown = 0f;
+
+    public float MaxWalkSlowdown = 0f;
+
+    public void SetIfMax(float valueSprint, float valueWalk)
+    {
+        MaxSprintSlowdown = MathF.Max(MaxSprintSlowdown, valueSprint);
+        MaxWalkSlowdown = MathF.Max(MaxWalkSlowdown, valueWalk);
+    }
+}