Fix small artifactual polygon ouputs

[PatBall1]

Annoying small polygons seem to be produce as an artefact of converting the mask to a polygon. Some area based filtering has already been applied but this is not ideal if smaller crowns are of interest.

Probably necessary to change this:
https://github.com/PatBall1/detectree2/blob/f996564bfcbaed1ff0ef13a63ea3e62f47252731/detectree2/models/outputs.py#L43C30-L43C30