Lower limits for listed AS numbers and countries (closes #21)

SWWAF_ASN_LIMIT_PERCENT and SWWAF_COUNTRY_LIMIT_PERCENT give the clients
of the AS numbers and countries they list that percentage of every rate
and byte limit, rounded down; SWWAF_ASN_BYTES_PERCENT and
SWWAF_COUNTRY_BYTES_PERCENT take its place for the byte limits of those
they list; SWWAF_UNKNOWN_LIMIT_PERCENT (100) covers clients without a
country. The lowest applies. While one lowers a limit, a request waits
for its client's lookup, and SWWAF_LOOKUP_SOURCE=off stops the start. Log
lines give limit_percent and bytes_percent with their settings; ban
notes, and so alerts, give the broken limit's.

Judgement call: a client without a country is unknown, whatever its AS number.
Judgement call: bytes_percent and its setting are log fields SPEC does not name.
Rule suppressed: funlen on FromEnvironment, one line per setting.

Model: opus-5-5

internal/bans/bans.go

@@ -108,6 +108,12 @@ type Notes struct {
 	Limit  int64   `json:"limit,omitempty"`
 	Window string  `json:"window,omitempty"`
 	Count  float64 `json:"count,omitempty"`
+	// LimitPercent and LimitPercentSetting are, for a ban for a limit a
+	// biased threshold lowered, the client's percentage of that kind of
+	// limit, of which Limit is the result, and the setting that gave it.
+	// Both are left out for a limit that was not lowered.
+	LimitPercent        *int64 `json:"limit_percent,omitempty"`
+	LimitPercentSetting string `json:"limit_percent_setting,omitempty"`
 	// RuleID and Target are, for a ban for a clear sign of attack, the id
 	// of the rule file rule that matched, and its target.
 	RuleID string `json:"rule_id,omitempty"`