Name log fields, metrics and the Core Rule Set package for what they are (closes #192)

The first half of the naming audit: names now say what they are. `internal/waf` is `internal/coreruleset`. Log fields, the action `blocked_by_core_rule_set`, the metric and the alert event say Core Rule Set. Timings end `_ms`. Percentages say of what, as `rate_limit_percent` and `bytes_limit_percent`. Setting names follow in #234.

Judgement call: `blocked_by_core_rule_set`, not the audit's `core_rule_set_blocked`, to match `blocked_by_block_rule`.
Trips a reader: an existing state file holding `waf_blocked` or the anomaly scope `watch` stops the start and must be removed. `SWW_ALERT_EVENTS` listing `waf_block` must list `core_rule_set_match`.

Model: opus-5-5

internal/discriminator/refusallimit.go

@@ -28,7 +28,7 @@ func (refusalLimit) check(_ context.Context, rq *request, now time.Time) *verdic
 		return nil
 	}
 
-	if !rq.attack && !rq.blockedByBlockRule && !rq.wafBlocked {
+	if !rq.attack && !rq.blockedByBlockRule && !rq.blockedByCoreRuleSet {
 		return nil
 	}
 
@@ -42,7 +42,7 @@ func (refusalLimit) check(_ context.Context, rq *request, now time.Time) *verdic
 	status := rq.out.status
 
 	switch rq.line.WouldAction {
-	case requestlog.ActionBlockedByBlockRule, requestlog.ActionWAFBlocked:
+	case requestlog.ActionBlockedByBlockRule, requestlog.ActionBlockedByCoreRuleSet:
 		status = http.StatusForbidden
 	case requestlog.ActionTemporarilyBanned, requestlog.ActionPermanentlyBanned:
 		status = cfg.BanResponse