Enhancement of Data Point Interaction Capabilities for Improved Analytical Depth

Dear FL Chart Contributors,

I hope this message finds you well. I am reaching out to propose an enhancement that could significantly augment the analytical utility of the FL Chart library. Having utilised your library extensively, I've found it to be remarkably versatile and user-friendly. However, there is an opportunity to deepen the user interaction with individual data points across various chart types.

**Issue Description:**
Currently, the interaction with data points on charts such as LineChart and ScatterChart is somewhat limited. Users can tap on a point to perhaps see a tooltip, but the potential for interaction stops there. For analysts and data enthusiasts, the ability to further interrogate a data point could be invaluable. This could include functionalities such as drilling down into more detailed data, linking a point to another chart or dataset, or even custom actions defined by the developer.

**Proposed Solution:**
I suggest we enhance the data point interaction model to include:
- A callback mechanism when a data point is long-pressed, allowing developers to define custom actions.
- The ability to link data points to secondary datasets or charts, enabling a drill-down capability.
- An expanded tooltip system that can display more detailed information, including metadata associated with data points.

**Benefits:**
- This enhancement would empower users to perform more detailed data analysis directly within the charts.
- It would add an interactive dimension to data presentation, making it more engaging and informative.
- Developers would have the flexibility to create a more interactive and integrated data visualisation experience.

I believe this feature could be a substantial addition to the FL Chart library, aligning with the ethos of providing a highly customisable and feature-rich charting experience. I am keen to hear your thoughts on this proposal and would be delighted to contribute to the discussion and development process.

Thank you for considering this enhancement. Your dedication to the FL Chart project is greatly appreciated by the community.

Best regards,
yihong1120

Start by reviewing the existing data-point interaction and tooltip behavior for LineChart and ScatterChart. The proposal combines long-press callbacks, linked datasets or charts, and expanded metadata, so the scope and acceptance criteria need to be clarified before identifying the relevant entry points and tests.

Written by the indexing model from the issue text.