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/request.go

@@ -138,6 +138,15 @@ func (h *handler) startRequest(
 	return rq
 }
 
+// addTag adds tag to the request's tags, which stay sorted and hold each tag
+// once.
+func (rq *request) addTag(tag string) {
+	at, found := slices.BinarySearch(rq.line.Tags, tag)
+	if !found {
+		rq.line.Tags = slices.Insert(rq.line.Tags, at, tag)
+	}
+}
+
 // requestHeaders returns the headers of r that names lists, by name in
 // lower case, each with its values joined by ", ". Authorization, Cookie
 // and Set-Cookie are never among them, whatever names says.