Blocklists and an AS percentage file fetched by URL (closes #29)

SWWAF_BLOCKLIST_URLS names lists of addresses and netblocks, fetched every
SWWAF_BLOCKLIST_REFRESH (24h, never under 1h). The last good copy is kept
whole in reputation.json and used while a fetch fails and across restarts.
SWWAF_BLOCKLIST_ACTION denies, limits or only logs a listed client; the log
line names the lists, each raises reputation_hit, and a failed fetch raises
source_failure. SWWAF_ASN_LIMIT_PERCENT_URL is fetched the same way and
counts as SWWAF_ASN_LIMIT_PERCENT does, the lower winning.

Judgement call: a restart fetches only lists whose copy is due.
Judgement call: a failed fetch is retried after the refresh, not sooner.
Not done: ban notes do not name the lists yet.

Model: opus-5-5

internal/proxy/biased_test.go

@@ -310,6 +310,7 @@ func TestRequestWaitsForItsLookupWhileABiasedThresholdIsSet(t *testing.T) {
 		{asnBytesPercent, asnDEHalf, true},
 		{countryBytesPercent, countryDEHalf, true},
 		{unknownLimitPercent, "99", true},
+		{asnLimitPercentURL, asnURL, true},
 		// At 100, its default, it lowers no limit.
 		{unknownLimitPercent, "100", false},
 	} {