[Feature Request] RadarChartTitle

I want the RadarChartTitle to be a widget, not a simple string. For example, I would like to use a widget called Text.rich, and the top of the text can be divided into blue under purple. If there is a feature like this, could you please let me know?..

Start by locating RadarChartTitle and reviewing how the radar chart currently accepts and renders its title. Check whether Flutter's Text.rich can be supported as the title widget, then verify that rich text styling appears correctly above the radar chart. Done means RadarChartTitle accepts a widget instead of only a string without breaking existing title usage.

Written by the indexing model from the issue text.