Offset radius for each section

Please add support for adding offset radius for each section.

This helps to add offset to the section to obtain result shown in image:


Start by locating the chart section implementation in the fl_chart codebase and compare its current rendering with the linked image. Determine which section API and rendering path control radius, then verify that different sections can receive different offsets and that existing chart behavior remains unchanged.

Written by the indexing model from the issue text.