Moved logic of collapsing songs into albums to model package

(it should really be called domain.... maybe will rename it later)

utils/number/number.go

@@ -0,0 +1,31 @@
+package number
+
+import "golang.org/x/exp/constraints"
+
+func Min[T constraints.Ordered](vs ...T) T {
+	if len(vs) == 0 {
+		var zero T
+		return zero
+	}
+	min := vs[0]
+	for _, v := range vs[1:] {
+		if v < min {
+			min = v
+		}
+	}
+	return min
+}
+
+func Max[T constraints.Ordered](vs ...T) T {
+	if len(vs) == 0 {
+		var zero T
+		return zero
+	}
+	max := vs[0]
+	for _, v := range vs[1:] {
+		if v > max {
+			max = v
+		}
+	}
+	return max
+}