FlGridData control length of vertical and horizontal lines

Being able to control the length of the horizontal and vertical grid lines would be nice. It is common to have a short tic on both x- and y- axis next to the value not necessarily a line from top to bottom,
Thanks for an excellent package!!

Start by locating FlGridData and the grid-rendering entry point in the fl_chart package. Check how horizontal and vertical lines are currently drawn, then define and verify configurable lengths that support short axis ticks as well as full grid lines.

Written by the indexing model from the issue text.