Set variable formats for STATA when specified

[seidelma]

When converting data from CSV with a JSON metadata file to STATA, the variable formats were being dropped. This caused STATA not to display the variables correctly, as described in #312, to wit:

. use "stata_repro"
((null))

. describe

Contains data from stata_repro.dta
 Observations:             2                  (null)
    Variables:             3                  24 Oct 2024 15:08
-----------------------------------------------------------------------
Variable      Storage   Display    Value
    name         type    format    label      Variable label
-----------------------------------------------------------------------
permno          double  %10.0g                CRSP permno (permno)
date            long    %12.0g                Day of last price observation (date)
eom             long    %12.0g                End of month (eom)
-----------------------------------------------------------------------

The date and eom fields should be of type "DATE" (and permno should be "UNSPECIFIED"), as specified in the .json file.

With this change, STATA now recognizes the data display format, eg:

. use "output"
((null))

. describe

Contains data from output.dta
 Observations:             2                  (null)
    Variables:             3                  28 Oct 2024 12:41
-----------------------------------------------------------------------
Variable      Storage   Display    Value
    name         type    format    label      Variable label
-----------------------------------------------------------------------
permno          double  %9.0f                 CRSP permno (permno)
date            long    %td                   Day of last price observation (date)
eom             long    %td                   End of month (eom)
-----------------------------------------------------------------------
Sorted by:

. list

     +--------------------------------+
     | permno        date         eom |
     |--------------------------------|
1. |  10107   31jan2020   31jan2020 |
2. |  10107   28feb2020   29feb2020 |
     +--------------------------------+

[FlipperPA]

Thank you @seidelma! This fixes #312. I've compiled and confirmed.