Byte limits per client over a minute, an hour and a day (closes #20)

SWWAF_BYTES_LIMIT_PER_MINUTE, _PER_HOUR and _PER_DAY (10G, 20G, 50G)
and SWWAF_BYTES_COUNT (both). A request's bytes are counted once its
answer has ended, for a request passed to the app that the rate limits
count; what a WebSocket carries each way, once it closes. Bytes over a
limit ban the client as a broken rate limit does, and cut nothing
short. clients.json keeps the byte buckets, the log line's counts carry
the byte totals, ban notes say what the limit is on, and the limit hits
metric is labelled by kind.

Judgement call: limit_hit names a byte window minute_bytes, hour_bytes
or day_bytes, as counts names the byte totals.
Judgement call: in observe mode, the bytes of a request enforce mode
would have refused are not counted.

Model: opus-5-5

internal/ratelimit/snapshot_test.go

@@ -64,6 +64,7 @@ func TestLoadEmptiesBucketsWhoseTimeHasPassed(t *testing.T) {
 
 	limiter := ratelimit.New(ratelimit.Limits{})
 	limiter.Count(client, start)
+	limiter.CountBytes(client, start, 5)
 	limiter.AddToHistory(client, start, ratelimit.Request{Forwarded: true})
 
 	loaded := func(now time.Time) ratelimit.Client {
@@ -76,19 +77,25 @@ func TestLoadEmptiesBucketsWhoseTimeHasPassed(t *testing.T) {
 	}
 
 	// Two minutes on, the window that ends then covers neither of the
-	// minute's buckets, which are emptied; the hour's and the day's stay,
-	// and so does the history.
+	// minute's buckets, of requests and of bytes, which are emptied; the
+	// hour's and the day's stay, and so does the history.
 	got := loaded(start.Add(2 * time.Minute))
 	if got.Minute != (ratelimit.Buckets{}) || got.Hour.Current != 1 ||
 		got.Day.Current != 1 || got.History.Requests != 1 {
 		t.Errorf("loaded two minutes on as %+v", got)
 	}
 
+	if got.MinuteBytes != (ratelimit.Buckets{}) || got.HourBytes.Current != 5 ||
+		got.DayBytes.Current != 5 {
+		t.Errorf("loaded two minutes on with buckets of bytes %+v, %+v and %+v",
+			got.MinuteBytes, got.HourBytes, got.DayBytes)
+	}
+
 	// A moment before, the window still covers some of the earlier one.
 	got = loaded(start.Add(2*time.Minute - time.Nanosecond))
-	if got.Minute.Current != 1 {
-		t.Errorf("loaded just under two minutes on with minute buckets %+v",
-			got.Minute)
+	if got.Minute.Current != 1 || got.MinuteBytes.Current != 5 {
+		t.Errorf("loaded just under two minutes on with minute buckets %+v and %+v",
+			got.Minute, got.MinuteBytes)
 	}
 }