Pedestrians near Salesforce Tower in San Francisco, California, on Wednesday, Jan. 25, 2023.Marlena Sloss | Bloomberg | Getty ImagesArtificial intelligence has been a big boon for San Francisco real estate. But not enough of one to make up for the broader struggle across the market.The vacancy rate for San Francisco office space reached a fresh record of 34.5% in the second quarter, according to a report Monday from commercial real estate firm Cushman & Wakefield. That's up from 33.9% in the fir...