Keep options in a fixed order, and say which block a diff hunk is in

Options of a block (server options, a view, a zone) are listed and
written grouped by topic, alphabetical within a group, so the same
option is in the same place everywhere. Top-level statements keep the
order they were added in.

named.conf diffs add the enclosing blocks to each hunk header, like
git's function context: @@ -50,6 +49,8 @@ view "internal" {.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/model/optorder_test.go

@@ -0,0 +1,40 @@
+package model
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestScopedOptionsOrder(t *testing.T) {
+	s := NewState()
+	add := func(scope string, names ...string) {
+		for i, n := range names {
+			id := int64(len(s.Options) + 1)
+			s.Options[id] = &Option{ID: id, Scope: scope, Name: n, Position: i}
+		}
+	}
+	// Added in an arbitrary order; listen-on twice.
+	add(ScopeView, "zzz-unknown", "forwarders", "listen-on", "recursion", "dnssec-validation", "aaa-unknown", "allow-query", "forward", "directory", "listen-on", "allow-transfer")
+	var got []string
+	for _, o := range s.ScopedOptions(ScopeView, 0) {
+		got = append(got, o.Name)
+	}
+	want := "directory listen-on listen-on allow-query forward forwarders recursion dnssec-validation allow-transfer aaa-unknown zzz-unknown"
+	if strings.Join(got, " ") != want {
+		t.Errorf("order:\n got %s\nwant %s", strings.Join(got, " "), want)
+	}
+	// An option given twice keeps the order it was added in.
+	l := s.ScopedOptions(ScopeView, 0)
+	if l[1].Position > l[2].Position {
+		t.Error("repeated listen-on swapped")
+	}
+	// Top-level statements stay as entered.
+	add(ScopeTopLevel, "logging", "acl", "key")
+	got = nil
+	for _, o := range s.ScopedOptions(ScopeTopLevel, 0) {
+		got = append(got, o.Name)
+	}
+	if strings.Join(got, " ") != "logging acl key" {
+		t.Errorf("top level: %v", got)
+	}
+}