Kids are falling far behind in school because of covid, and desperately need good teachersto catch up. But across the state, districts are struggling to fill vacancies. Here’s one easy way to help fix the problem: End New Jersey’s residency law that bars districts from hiring candidates who live in neighboring states. We’ve seen how absurd this game can get under current law.The Somerville school board hired a private investigator in 2018 to track an English teacher with 12 years of experienceand prove that she’d moved in with her boyfriend in Pennsylvania, a no-no. But the biggest problem wit…