Request tags, with refusing and limits per tag (closes #175)

Each request gets sorted tags from the lookup, new address lists, the
reputation sources and the rule matches, logged as `tags`. New settings:
`SWW_TAG_LISTS`, `SWW_TAG_DENY`, `SWW_TAG_LIMIT_PERCENT`. They replace
`SWW_ASN_LIMIT_PERCENT`, `SWW_COUNTRY_LIMIT_PERCENT` and
`SWW_DENIED_COUNTRIES`. New heuristics `tag_lists` and `tag_deny`; the
latter runs before the rate limits and again after the Core Rule Set.

Model: opus-5-5

internal/discriminator/ratelimits_test.go

@@ -136,7 +136,7 @@ func TestRateLimitExemptPathsAreNeitherCountedNorRefused(t *testing.T) {
 		rateLimitPerMinute:   "1",
 		rateLimitExemptPaths: "/assets/,/favicon.ico",
 		denyNets:             denied,
-		deniedCountries:      "kp",
+		tagDeny:              denyKP,
 	})
 
 	// The answers are kept before the requests, so that none waits for
@@ -162,12 +162,12 @@ func TestRateLimitExemptPathsAreNeitherCountedNorRefused(t *testing.T) {
 	// /assets/, and breaks the limit.
 	s.request(client, "/assets", http.StatusForbidden, requestlog.ActionRateLimited)
 
-	// A ban, SWW_DENY_NETS and the country lists still refuse a path
-	// under a prefix.
+	// A ban, SWW_DENY_NETS and SWW_TAG_DENY still refuse a path under a
+	// prefix.
 	s.request(client, "/assets/app.js", http.StatusForbidden, requestlog.ActionBanned)
 	s.request(denied, "/assets/app.js", http.StatusForbidden, requestlog.ActionDenied)
 	s.request(fromKP, "/assets/app.js",
-		http.StatusForbidden, requestlog.ActionCountryDenied)
+		http.StatusForbidden, requestlog.ActionDenied)
 }
 
 func TestRateLimitCountsPathsThatAreNotExempt(t *testing.T) {