Once upon a time you could enter the first floor of Boston’s Copley Square public library and escape having to listen to the self-promotional chatter of corporate-sponsored or underwritten radio show hosts and their Establishment or celebrity guests, while you read a book or sat in front of your laptop. Yet nowadays, the two former longtime WTKK-FM commercial radio talk show hosts that the WGBH Educational foundation hired in 2013 to co-host its “Boston Public Radio” daily morning show, Margery Eagan and Jim Braude, are also broadcasting their 11:00 a.m. to 2:00 p.m.