A top California lawmaker unveiled a $1 billion proposal on Tuesday to fund free public preschool for all children in the most populous U.S. state, the latest challenge by Democratic leaders to fiscal restraints imposed by Governor Jerry Brown, Reuters reports. The plan by Senate Democratic leader Darrell Steinberg to offer pre-kindergarten to California 4-year-olds comes as he and other Democratic lawmakers try to push Brown to raise spending on social services, including education, in next year’s budget…