Extracts the dependent variable name and regressor names from the formula.
Evaluates L(), D(), Lrange() calls by applying them panel-aware
and adding the resulting columns to the panel.
.parse_dcce_formula(formula, panel, unit_var, time_var)A list with y_name and x_names.
A formula.
A panel data.frame.
Character: unit variable name.
Character: time variable name.