Add an example using custom distance for nearest search

[aprokop]

No description provided.

[dalg24]

I would drop the callback to reduce complexity and explore defining struct MyPoint { float x, y; };

[dalg24]

Why did you elect to get distances out instead of indices?
I suspect indices would make it more obvious that the distance metric was changed.
I find the use of both a custom geometry with specialized distance computation mixed with a callback that recomputes the distance potentially confusing.

[aprokop]

I chose distances so that a user can see that the computed distances are indeed the custom ones. Computing just the found indices seems insufficient to me, as it still does not confirm that we can get the correct distance in the callback.

[aprokop]

explore defining struct MyPoint { float x, y; };

The whole point is for a user to not define their own type. The only thing that's necessary is to have a separate type for disambiguation during the dispatch.