Say the class of what a change plan moves, so a fix's budget follows its modules (issue 403)

The issue tracker holds a fix to the budget of the slowest-budgeted module it
moves, and gives none to a fix that moves no module (hq ADR 0313 §2). The
walk's class covers every merge a walk carries; the plan's class is the
change's own: core, leaf, or none.

cmd/mesh-controller/batches.go

@@ -1109,6 +1109,16 @@ const resolverSeat = "mesh-dns-resolver"
 // classOf is a walk's class (novox/hq ADR 0282 decision 1): core when it walks a module on the controller's own
 // path or one holding the mesh's resolver, leaf otherwise.
 func classOf(walk inventory.Plan, entries []inventory.Entry) string {
+	modules := make([]string, 0, len(walk.Modules))
+	for m := range walk.Modules {
+		modules = append(modules, m)
+	}
+	return classOfModules(modules, entries)
+}
+
+// classOfModules is the class of modules moved together: core when one is on the controller's own path or holds
+// the mesh's resolver, leaf otherwise (ADR 0282 decision 1).
+func classOfModules(modules []string, entries []inventory.Entry) string {
 	resolvers := map[string]bool{}
 	for _, e := range entries {
 		for _, c := range e.Manifest.Claims {
@@ -1117,7 +1127,7 @@ func classOf(walk inventory.Plan, entries []inventory.Entry) string {
 			}
 		}
 	}
-	for m := range walk.Modules {
+	for _, m := range modules {
 		if _, own := onTheControllersPath[m]; own || resolvers[m] {
 			return inventory.ClassCore
 		}