perf: in-place filtering in RateLimiter to reduce GC pressure

internal/platform/httpx/limits.go

@@ -63,14 +63,15 @@ func (rl *RateLimiter) Allow(key string) bool {
 	sw.mu.Lock()
 	defer sw.mu.Unlock()
 
-	// Remove expired tokens
+	// Remove expired tokens using in-place filtering to avoid GC pressure.
-	var valid []time.Time
+	n := 0
 	for _, t := range sw.tokens {
 		if t.After(cutoff) {
-			valid = append(valid, t)
+			sw.tokens[n] = t
+			n++
 		}
 	}
-	sw.tokens = valid
+	sw.tokens = sw.tokens[:n]
 
 	if len(sw.tokens) >= rl.limit {
 		return false