Take in an admin's edits of the state files while running (closes #68)

smallwebwaf watches SWWAF_STATE_DIR with fsnotify and takes in a saved
edit of a state file in place of what it held. It knows its own writes
by the SHA-256 of what it last read or wrote; each write first takes in
an edit made since. An edit that does not parse is renamed to
<name>.bad at the next write. Each edit taken in or set aside is logged
and counted. Every ban on a netblock is checked, and the next ban is
worked out from the one that ended last. README.md says how to add and
lift a ban.

Judgement call: a broken edit is set aside at the next write, since an
editor's file can be read half written.

Model: opus-5-5

internal/lookup/lookup.go

@@ -197,19 +197,21 @@ func (g *GeoJS) Snapshot() []Answer {
 	return answers
 }
 
-// Load keeps answers read from lookups.json, in a GeoJS that keeps none
-// yet, in the order they were last used, so that the one used longest
+// Load keeps answers read from lookups.json, in place of the answers it
+// keeps, in the order they were last used, so that the one used longest
 // ago is dropped first. Answers GeoJS gave keepFor ago or more are
 // dropped.
 func (g *GeoJS) Load(answers []Answer) {
-	g.mu.Lock()
-	defer g.mu.Unlock()
-
 	answers = slices.Clone(answers)
 	slices.SortStableFunc(answers, func(a, b Answer) int {
 		return a.Used.Compare(b.Used)
 	})
 
+	g.mu.Lock()
+	defer g.mu.Unlock()
+
+	g.answers.Purge()
+
 	now := g.now()
 
 	for _, answer := range answers {