test data

PNG&csv test data, included batched uncompreesed preprocess file.
Directory structure from build root should look like this after extraction:

> ls data
    Directory: W:\dev\zig\zig-nnet\data

Mode                 LastWriteTime         Length Name
----                 -------------         ------ ----
d-----         17-Mar-23     22:37                digits
-a----         07-Dec-23      2:11      172683028 test.batch
-a----         07-Dec-23      2:11      402927028 train.batch