SANTA CLARA, Calif. — Brandon Aiyuk won’t stop catching passes at 49ers training camp. Yes, that is the third-year wide receiver’s job, but the sheer number of catches he’s made so far in training camp — and the level of difficulty on some of them — has been revelatory. High passes, low passes, passes in front of him, and passes behind him – Aiyuk is reeling in everything, putting his prodigious and unique 81-inch wingspan to good use. The 49ers’ defense might be the best in the NFL. The team’s secondary, linebackers, and defensive line can all claim they are elite. It’s not a fun group to pra…