Feature Request - Draggable Points

[andy-edvalson]

So far super impressed with this library!

Problem

FL Chart currently doesn't support dragging data points, which limits its use
for interactive data editing applications (scheduling, profile editing, etc.)

Proposed Solution

Add optional drag-and-drop functionality to LineChart that allows users to:

• Select data points by tapping
• Drag selected points to new positions
• Receive callbacks with updated point positions
• [Optional] Validate moves via callbacks (e.g., prevent out-of-bounds updates)

Use Case

I've implemented this in a pretty proprietary fashion, including gesture detection, throttling, nearest point detection, and final position capture for a production app and might be able to contribute it back.

Would it be helpful if I attempt to adapt it to a PR?