AbuseIPDB scores for clients that committed an offence, within a daily budget (closes #105)

With SWWAF_ABUSEIPDB_KEY set, a client whose history counts an offence
(a broken limit, a ban rule's match or a block rule's refusal, counted
by kind) is checked in the background, at most
SWWAF_ABUSEIPDB_DAILY_BUDGET checks a day, the count kept in
reputation.json. A client, an IPv4 address or an IPv6 /64, is checked by
the address it sent from, and its score serves all its addresses. A
score at or over SWWAF_ABUSEIPDB_MIN_SCORE is a hit for
SWWAF_REPUTATION_ACTION, logged as abuseipdb and alerted with its score.
A failure or the used-up budget gives no score and raises
source_failure. The key goes only in the Key header.

Judgement call: the budget's day is UTC; AbuseIPDB documents no reset time.
Judgement call: each check sent spends budget; a minute's pause after a failure.

Model: opus-5-5

internal/ratelimit/ratelimit.go

@@ -118,8 +118,12 @@ type Responses struct {
 
 // Offences are a client's offences, by kind.
 type Offences struct {
-	// Limit is its requests that broke a rate limit or a byte limit.
-	Limit int64 `json:"limit"`
+	// Limit is its requests that broke a rate limit or a byte limit,
+	// Attack those that matched a ban rule, a clear sign of attack, and
+	// RuleBlocked those a block rule refused.
+	Limit       int64 `json:"limit"`
+	Attack      int64 `json:"attack"`
+	RuleBlocked int64 `json:"rule_blocked"`
 }
 
 // Request is what a client's history keeps of one of its requests.
@@ -137,8 +141,11 @@ type Request struct {
 	RequestBytes  int64
 	ResponseBytes int64
 	// BrokeLimit is true for a request that broke a rate limit or a byte
-	// limit.
-	BrokeLimit bool
+	// limit, Attack for one that matched a ban rule, and RuleBlocked for
+	// one a block rule refused.
+	BrokeLimit  bool
+	Attack      bool
+	RuleBlocked bool
 }
 
 // New returns a Limiter for limits, with no client counted yet.
@@ -258,6 +265,14 @@ func (l *Limiter) AddToHistory(client netip.Prefix, now time.Time, r Request) {
 	if r.BrokeLimit {
 		h.Offences.Limit++
 	}
+
+	if r.Attack {
+		h.Offences.Attack++
+	}
+
+	if r.RuleBlocked {
+		h.Offences.RuleBlocked++
+	}
 }
 
 // AddLookup gives client's history its AS number, AS name and country, as