util/set: add some useful utility functions for Set (#9535)

Also give each type of set its own file.

Updates #cleanup

Signed-off-by: Chris Palmer <cpalmer@tailscale.com>

util/set/set_test.go

@@ -3,7 +3,10 @@
 
 package set
 
-import "testing"
+import (
+	"slices"
+	"testing"
+)
 
 func TestSet(t *testing.T) {
 	s := Set[int]{}
@@ -21,4 +24,41 @@ func TestSet(t *testing.T) {
 	if s.Len() != 2 {
 		t.Errorf("wrong len %d; want 2", s.Len())
 	}
+
+	more := []int{3, 4}
+	s.AddSlice(more)
+	if !s.Contains(3) {
+		t.Error("missing 3")
+	}
+	if !s.Contains(4) {
+		t.Error("missing 4")
+	}
+	if s.Contains(5) {
+		t.Error("shouldn't have 5")
+	}
+	if s.Len() != 4 {
+		t.Errorf("wrong len %d; want 4", s.Len())
+	}
+
+	es := s.Slice()
+	if len(es) != 4 {
+		t.Errorf("slice has wrong len %d; want 4", len(es))
+	}
+	for _, e := range []int{1, 2, 3, 4} {
+		if !slices.Contains(es, e) {
+			t.Errorf("slice missing %d (%#v)", e, es)
+		}
+	}
+}
+
+func TestSetOf(t *testing.T) {
+	s := SetOf[int]([]int{1, 2, 3, 4, 4, 1})
+	if s.Len() != 4 {
+		t.Errorf("wrong len %d; want 2", s.Len())
+	}
+	for _, n := range []int{1, 2, 3, 4} {
+		if !s.Contains(n) {
+			t.Errorf("should contain %d", n)
+		}
+	}
 }