Raise an error when loading points and there are already particles picked (by default)

[kevinyamauchi]

Currently, with the point loading widget, if one has already picked some particles, they will be silently overwritten. I think this could lead to accidental deletion of work-in-progress picks. I think we should make this an error by default with an option to overwrite existing points.

[kevinyamauchi]

To implement this, we would need:

1. to add an additional boolean input argument (e.g., overwrite_existing) to _load_star_file() (linked below) that if set True would overwrite the existing vector and points layer data.
2. add a check that if overwrite_existing is False, if self.surface_picker.points_layer.data has length > 0, raise an error.

surforama/src/surforama/gui/qt_point_io.py

Lines 53 to 63 in 431c368

	def _load_star_file(self, file_path: Path):
	"""Load oriented points from a star file and add them
	to the viewer.
	"""
	if self.surface_picker.enabled is False:
	show_warning("The surface picker must be enabled to load a file.")
	return
	# get the points data
	point_coordinates, features_table = (
	load_points_layer_data_from_star_file(file_path=file_path)
	)