Function evaluate_with_two_bindings 

pub fn evaluate_with_two_bindings(
    expr: &ValueExpr,
    variables: &HashMap<String, Value>,
    var1: &str,
    value1: &Value,
    var2: &str,
    value2: &Value,
) -> Result<Value, ExecutionError>

Evaluate an expression with two extra variable bindings. Used for reduce operations with accumulator and item variables.