PARIS—Luca Funaro, a 32-year-old with a rare genetic illness, suffered through this month’s record-breaking heat wave in his apartment in the French capital without an air conditioning system. His neighbors won’t allow one. They have refused his requests to install a unit in the courtyard of his building in the Marais, a bustling neighborhood in central Paris. They said the device would be too loud. Funaro, who relies on a wheelchair and breathes with a ventilator, has taken the neighbors to court, his family spending thousands of euro on a legal battle that has lasted two years and counting. “If…