Keep the bans, the clients and GeoJS's answers in state files (closes #17)

smallwebwaf now copies its state to bans.json, clients.json and
lookups.json in SWWAF_STATE_DIR, as "Persistent state" in SPEC.md
describes, and reads them back at start, so a restart lifts no ban and
gives no client a fresh allowance. Each client gains a history, and a
ban's notes count the netblock's requests. bans.json is written
SWWAF_STATE_WRITE_DELAY after a ban, and every file every
SWWAF_STATE_COUNTER_INTERVAL and at the stop. A ban read back is masked
to its netblock and refuses every client in it. A file that does not
parse, an unknown version, an entry without a field it needs, or an
unwritable directory stops the start.

Deviation: no AS number or name, and no ban cause, reason or lifting yet.

Model: opus-5-5

internal/smallwebwaf/healthcheck_test.go

@@ -24,12 +24,14 @@ func TestHealthCheck(t *testing.T) {
 
 	out := &output{}
 	exited := make(chan int, 1)
+	settings := map[string]string{
+		listenAddr:  localhost + ":0",
+		upstreamURL: app.URL,
+		stateDir:    t.TempDir(),
+	}
 
 	go func() {
-		exited <- run(ctx, map[string]string{
-			listenAddr:  localhost + ":0",
-			upstreamURL: app.URL,
-		}, out)
+		exited <- run(ctx, settings, out)
 	}()
 
 	addr, _ := out.line(t, "msg", "starting")["address"].(string)