refactor: move modeltypes to own folder, move IDs to file of respective type

PluralKit.Core/Models/PKSwitch.cs

@@ -1,6 +1,33 @@
 using NodaTime;
 
+
+
 namespace PluralKit.Core {
+
+    public readonly struct SwitchId: INumericId<SwitchId, int>
+    {
+        public int Value { get; }
+
+        public SwitchId(int value)
+        {
+            Value = value;
+        }
+
+        public bool Equals(SwitchId other) => Value == other.Value;
+
+        public override bool Equals(object obj) => obj is SwitchId other && Equals(other);
+
+        public override int GetHashCode() => Value;
+
+        public static bool operator ==(SwitchId left, SwitchId right) => left.Equals(right);
+
+        public static bool operator !=(SwitchId left, SwitchId right) => !left.Equals(right);
+
+        public int CompareTo(SwitchId other) => Value.CompareTo(other.Value);
+        
+        public override string ToString() => $"Switch #{Value}";
+    }
+
     public class PKSwitch
     {
         public SwitchId Id { get; }