Prospective teachers are interviewing on the spot and some are getting offers at winter and spring job fairs across Contra Costa County. Last month, dozens of candidates met recruiters at Alhambra High School in Martinez, where many districts competed for prospective employees amid a national teacher shortage. And from 9 a.m. to noon this Saturday, West Contra Costa Unified School District will hold a job fair at DeJean Middle School. WCCUSD has been hit hard by the shortage. At the…