Architect’s rendering of Market Street Place. The backhoe is digging. New fencing is up. And construction crews are on site. Market Street Place, the most highly anticipated new retail development since the expanded Westfield San Francisco Centre opened in 2006, is off and running. The $150 million, 250,000 square-foot retail project doesn’t have any tenants yet, but advocates of the much-hyped Mid-Market revival, including Mayor Ed Lee and Supervisor Jane Kim, hope that the development will fill in a key derelict block between Fifth and Sixth streets. On Wednesday the developer, Cypress Equities, will celebrate the official groundbreaking “Our contractor is mobilized and we are going,” said Cypress Equities CEO