[Feature] Circle brush for scatter plot

### What problem does this feature solve?

Hello,
I am really in need of applying circle brushing, as there are the box and lasso. Are there any fragment code or docs on how to implement a circle or ellipse brush for scatter plot please.
Thanks

### What does the proposed API look like?

Ideally similar to box and lasso brushes.

Review the existing box and lasso brush APIs and documentation first; the issue does not name files or tests. Clarify the circle or ellipse interaction and selection behavior, then define an analogous API for scatter plots and add coverage for the new behavior.

Written by the indexing model from the issue text.