StaminaSystem to SharedStaminaSystem (#37199)

* Init Commit

* Partial class

* Hands system slipped through

Content.Shared/Damage/Systems/SharedStaminaSystem.Modifier.cs

@@ -0,0 +1,52 @@
+using Content.Shared.Damage.Components;
+
+namespace Content.Shared.Damage.Systems;
+
+public partial class SharedStaminaSystem
+{
+    private void InitializeModifier()
+    {
+        SubscribeLocalEvent<StaminaModifierComponent, ComponentStartup>(OnModifierStartup);
+        SubscribeLocalEvent<StaminaModifierComponent, ComponentShutdown>(OnModifierShutdown);
+    }
+
+    private void OnModifierStartup(EntityUid uid, StaminaModifierComponent comp, ComponentStartup args)
+    {
+        if (!TryComp<StaminaComponent>(uid, out var stamina))
+            return;
+
+        stamina.CritThreshold *= comp.Modifier;
+    }
+
+    private void OnModifierShutdown(EntityUid uid, StaminaModifierComponent comp, ComponentShutdown args)
+    {
+        if (!TryComp<StaminaComponent>(uid, out var stamina))
+            return;
+
+        stamina.CritThreshold /= comp.Modifier;
+    }
+
+    /// <summary>
+    /// Change the stamina modifier for an entity.
+    /// If it has <see cref="StaminaComponent"/> it will also be updated.
+    /// </summary>
+    public void SetModifier(EntityUid uid, float modifier, StaminaComponent? stamina = null, StaminaModifierComponent? comp = null)
+    {
+        if (!Resolve(uid, ref comp))
+            return;
+
+        var old = comp.Modifier;
+
+        if (old.Equals(modifier))
+            return;
+
+        comp.Modifier = modifier;
+        Dirty(uid, comp);
+
+        if (Resolve(uid, ref stamina, false))
+        {
+            // scale to the new threshold, act as if it was removed then added
+            stamina.CritThreshold *= modifier / old;
+        }
+    }
+}