code: def all_providers_cnpj(df):
      
      cnpj_list = []
  
      for _, items in df.groupby('PRONAC'):
          unique_cnpjs = items['nrCNPJCPF'].unique()
          cnpj_list += list(unique_cnpjs)
  
      return pd.DataFrame(cnpj_list)
docs: Return CPF/CNPJ of all providers
      in database.