fix: CircleLayer not updating on pan

[Robbendebiene]

Since version 6.0.1 the circle layer is not updated properly any more.

This was introduced as a side effect of: 117f254#diff-5d1e8506fe899e135910abbab2ef61ca6b4fde4e34f60b80b0fd85204ae485baL40-L47

Before	After
before.webm	after.webm

This can also be tested using the example app's circle layer page by adding an AnimatedSwitcher around the CircleLayer.

AnimatedSwitcher(
  duration: Duration(milliseconds: 300),
  child: CircleLayer(circles: circleMarkers),
),

While looking at it the circle layer could certainly get some more love (like caching the grouped circles), but I currently don't have time for any additional optimizations.

[josxha]

Thanks for your pull request. I can reproduce this issue with the as described by wrapping the CircleLayer with an AnimatedSwitcher. It doesn't occur when using the CircleLayer directly.
I did a performance test to see how much time the check takes and it seems to have no noticable penatly.

Aufzeichnung.2023-11-23.141027.mp4

The PR looks good to me, however I'd like to have another code review before we can merge.

[TesteurManiak]

LGTM too!