adds support for comprehensions

[drizk1]

fixes #90 with minimal change to parsing_function

julia> df = DataFrame(ID1 = ["ID_1", "ID_23", "ID_456"])
3×1 DataFrame
 Row │ ID1    
     │ String 
─────┼────────
   1 │ ID_1
   2 │ ID_23
   3 │ ID_456

julia> @chain df begin 
                  @mutate(across(ID1, s -> split.(s, "_")))
                  @mutate(ID = [x[2] for x in ID1_function])
              end
3×3 DataFrame
 Row │ ID1     ID1_function                    ID        
     │ String  Array…                          SubStrin… 
─────┼───────────────────────────────────────────────────
   1 │ ID_1    SubString{String}["ID", "1"]    1
   2 │ ID_23   SubString{String}["ID", "23"]   23
   3 │ ID_456  SubString{String}["ID", "456"]  456