Ban the netblock of a client that breaks a rate limit, in memory (closes #18)

A request over a rate limit is refused with SWWAF_BAN_RESPONSE and bans
the client's netblock: an hour at first, three times the last ban when
broken again within a day of its end, permanent past seven days. The
ban ledger in internal/bans is checked after the static lists and
before the lookup, and the requests it refuses are not counted. A ban
resets the client's counters and carries notes holding the request
that broke the limit, as SPEC.md now says. At most SWWAF_MAX_BANS are
held. SWWAF_BAN_RESPONSE also answers SWWAF_DENY_NETS and the country
lists.

Judgement call: the six ban settings cannot be off.
Judgement call: a permanent ban's ban_expires is "permanent".

Model: opus-5-5

internal/ratelimit/ratelimit_test.go

@@ -54,6 +54,52 @@ func TestEachWindowRefusesAtItsLimitAndLetsTheClientBack(t *testing.T) {
 	}
 }
 
+func TestHitGivesTheLimitAndTheRequestsCounted(t *testing.T) {
+	t.Parallel()
+
+	limiter := ratelimit.New(ratelimit.Limits{PerMinute: limit, PerHour: limit})
+	client := netip.MustParsePrefix("203.0.113.9/32")
+	start := midnight()
+
+	for range limit {
+		_, over := limiter.Count(client, start)
+		if over {
+			t.Fatal("a request within the limit is over it")
+		}
+	}
+
+	// Over both limits; the minute's is named, with the four requests.
+	hit, over := limiter.Count(client, start)
+
+	want := ratelimit.Hit{Window: minute, Limit: limit, Requests: limit + 1}
+	if !over || hit != want {
+		t.Errorf("request over the limit gives %+v and %t, want %+v and true",
+			hit, over, want)
+	}
+}
+
+func TestResetSetsTheCountsBackToZero(t *testing.T) {
+	t.Parallel()
+
+	limiter := ratelimit.New(ratelimit.Limits{PerMinute: limit, PerDay: limit})
+	client := netip.MustParsePrefix("203.0.113.9/32")
+	start := midnight()
+
+	for range limit {
+		wantCount(t, limiter, client, start, "")
+	}
+
+	wantCount(t, limiter, client, start, minute)
+	limiter.Reset(client)
+
+	// At the same moment, the client has its whole allowance again.
+	for range limit {
+		wantCount(t, limiter, client, start, "")
+	}
+
+	wantCount(t, limiter, client, start, minute)
+}
+
 func TestClientBackAfterAWholeBucketIsWithinTheLimitAtOnce(t *testing.T) {
 	t.Parallel()
 
@@ -192,9 +238,9 @@ func wantCount(
 ) {
 	t.Helper()
 
-	got := limiter.Count(client, now)
-	if got != want {
+	hit, _ := limiter.Count(client, now)
+	if hit.Window != want {
 		t.Errorf("request from %s at %s is over %q, want %q",
-			client, now.Format(time.RFC3339), got, want)
+			client, now.Format(time.RFC3339), hit.Window, want)
 	}
 }