Add foundation

Toolkit.Foundation/Unit.cs

@@ -0,0 +1,29 @@
+namespace Toolkit.Foundation;
+
+public readonly struct Unit :
+    IEquatable<Unit>,
+    IComparable<Unit>,
+    IComparable
+{
+    private static readonly Unit value = new();
+
+    public static ref readonly Unit Value => ref value;
+
+    public static ValueTask<Unit> ValueTask => new(value);
+
+    public int CompareTo(Unit other) => 0;
+
+    int IComparable.CompareTo(object? obj) => 0;
+
+    public override int GetHashCode() => 0;
+
+    public bool Equals(Unit other) => true;
+
+    public override bool Equals(object? obj) => obj is Unit;
+
+    public static bool operator ==(Unit _, Unit __) => true;
+
+    public static bool operator !=(Unit _, Unit __) => false;
+
+    public override string ToString() => "()";
+}