Fix TypeError in ray_cast_by_proximity_2d degenerate edge

A degenerate edge (zero-length segment) caused an early `return`
of a tuple instead of continuing the loop, resulting in a
TypeError when snap.py iterated the result and tried to assign
`point["group"]` on a float.

Generated with the assistance of an AI coding tool.

src/bonsai/bonsai/tool/raycast.py

@@ -434,11 +434,8 @@ class Raycast(bonsai.core.tool.Raycast):
             seg_len_sq = sx * sx + sy * sy
 
             if seg_len_sq == 0.0:
-                # degenerate segment: return distance to p0
-                dx = px - p0x
-                dy = py - p0y
-                dist = math.hypot(dx, dy)
-                return dist, (p0x, p0y), 0.0
+                # degenerate segment: skip it
+                continue
 
             # project (p - p0) onto seg: t = dot(p-p0, seg) / |seg|^2
             apx = px - p0x