Handle formulas with simple expressions and cell references.
Implement evaluate_formulas(cells), where cells maps cell names such as A1 to numbers or formulas beginning with =. Support numeric literals, cell references, parentheses, unary signs, and +, -, *, and / with standard precedence. Return a mapping containing the evaluated numeric value of every cell. Inputs are valid and acyclic; referenced cells exist.
def evaluate_formulas(cells):