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/proxy/proxy_test.go

@@ -200,7 +200,7 @@ func startProxyWithGeoJS(
 func startProxyWithClock(
 	t *testing.T, appURL, geojsURL string, now func() time.Time,
 	env map[string]string,
-) (string, *output, *http.Server) {
+) (string, *output, *proxy.Server) {
 	t.Helper()
 
 	settings := map[string]string{"SWWAF_UPSTREAM_URL": appURL}