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/proxy/proxy_test.go

@@ -315,7 +315,7 @@ func newProxy(
 
 	var lookupFile *lookup.File
 
-	if cfg.LookupSource == "file" {
+	if cfg.LookupSource == fileSource {
 		lookupFile, err = lookup.OpenFile(lookup.FileParams{
 			Path: cfg.LookupDBPath, Now: now, ProcessLog: processLog, Alerts: alertQueue,
 		})