Add FIREWALL_LOG_TS_RE regex to parse timestamps from firewall log lines, implement firewall_log_seen_at to extract and convert log timestamps to UTC ISO format, add first_seen_at/last_seen_at/observed_at fields to flows in collect_packet_flows (AF_PACKET collector) with timestamp updates on flow aggregation, add timestamp fields to collect_flows (conntrack collector) and parse_firewall_log_line (