The fireworks are still a few days away, but travel for the July Fourth weekend is off to a booming start. The Transportation Security Administration said Friday that it screened more people on Thursday than it did on the same day in 2019, before the pandemic. Travelers so far seem to be experiencing fewer delays and canceled flights than they did earlier this week. But it’s still early. Leisure travel has bounced back this year, offsetting weakness in business travel and international flying. Still, the total number of people flying has not quite recovered fully to pre-pandemic levels.