Fixed #220, Rendering nested categories properly when Sampling Starts

[nithin4048-1]

Before fix recording:
https://github.com/user-attachments/assets/db0f0b7d-06cb-4483-9073-8075f6355fcb

After fix recording:
https://github.com/user-attachments/assets/7ed43c3b-00c7-4ff1-9d2e-4048b7651787

Fixes covered as part of this PR:

1. Leaf labels follow Highcharts native overlap behavior -> Previously, the plugin forced all leaf (x-axis) labels to display, causing them to overlap each other on dense charts. Now Highcharts handles label visibility natively, automatically hiding overlapping labels just like it does on a standard axis.

2. Text truncation with ellipsis for parent labels -> When there isn't enough horizontal space for a parent category label, the text is now truncated with an ellipsis ("...") instead of overflowing or overlapping adjacent labels. Labels are hidden entirely when the space is extremely tight and restored automatically when the chart is resized wider.

3. Grid lines no longer break on narrow charts with many bars -> Previously, when the chart was narrow and had dense data, grid separator lines would go missing or render incorrectly. This has been fixed.

4. Corrected grid positioning across all levels -> Grid lines for both leaf-level and parent-level separators were misaligned. Their positioning has been corrected so they render accurately at every depth.

5. Accurate parent grid separator placement -> Parent-level grid separators are now positioned based on the actual category tree structure rather than relying on rendered tick data, which could be incomplete when Highcharts hides labels. This ensures separators always appear at the correct boundaries.

6. Improved leaf label vertical centering -> Leaf labels are better centered within their grid row on grouped axes, while still respecting any custom distance set by the user.

[nithin4048-1]

Hi @pawelfus / @jedrzejruta ,
Request you to review this PR.
Attached the screen recording with all the details. Thanks!