The state is financing almost all of the cost of multiple school projects in Hartford, but investigators have zeroed in on the $150 million overhaul of Bulkeley High School on the city’s southside, according to public records and interviews with more than a half dozen people familiar with the project.In particular, the investigators appear interested in how Konstantinos Diamantis, the politically-influential former director of the state school financing program, persuaded Hartford to hire a second consultant and how that consultant, Construction Advocacy Professionals, was awarded the contract even though two competitors submitted lower bids.