By Hyunjoo Jin SAN FRANCISCO (Reuters) -Elon Musk’s move to buy Twitter for $44 billion has raised concerns about the depth of executive talent at his more valuable company, electric carmaker Tesla Inc, in case his attention is further divided by the social media platform. In announcing the deal on Monday, Musk called Twitter the world’s “digital town square” and talked about protecting free speech, but he also rekindled fears that a man who once acknowledged sleeping on the factory floor during the launch of the Model 3 sedan and last year talked of working “crazy hours” only has so much ener…