Add a helper set library to facilitate implementation of the new heal…

…th check procedure (#252)

This is the first PR in a series of [stacked
PRs](https://www.stacking.dev/), aimed ultimately at implementing the
features described in #181 and #207. The next PR in the stack can be
found at #259.

pkg/set/set.go

@@ -0,0 +1,29 @@
+package set
+
+type Set[E comparable] map[E]struct{}
+
+func New[E comparable](vals ...E) Set[E] {
+	s := Set[E]{}
+	for _, v := range vals {
+		s[v] = struct{}{}
+	}
+	return s
+}
+
+func (s Set[E]) Add(vals ...E) {
+	for _, v := range vals {
+		s[v] = struct{}{}
+	}
+}
+
+func (s Set[E]) Equals(other Set[E]) bool {
+	if len(s) != len(other) {
+		return false
+	}
+	for k := range s {
+		if _, has := other[k]; !has {
+			return false
+		}
+	}
+	return true
+}