Consistent Stack Border Radius for Bar Charts

### Feature Proposal

In stacked bar charts, Chart.js currently seems to render border radius individually for each dataset.

When the top bar of a stack is thin, that makes the entire stack appear “flat” or uneven at the top.

Example:


Would it be possible to add an option for border radius to be applied to the entire stack as a whole, rather than each individual dataset?

This would help visuals look more polished and consistent in cases like this, regardless of individual bar sizes.

Apologies if I missed an existing setting for this. I also made a couple quick (unsuccessful) attempts at a plugin, but this strikes me as something that would be nice if it was supported natively.

### Possible Implementation

_No response_