Fix #4014: Unassign annotation from all products before reassignment

The edit_assigned_product() function now removes the annotation from all
existing IfcRelAssignsToProduct relationships instead of just one, preventing
annotations from being incorrectly assigned to multiple products simultaneously.

This fixes issues where leader lines wouldn't update correctly because the
annotation retained old product assignments.

src/bonsai/bonsai/core/drawing.py

@@ -60,10 +60,21 @@ def edit_assigned_product(
 ) -> None:
     element = ifc.get_entity(obj)
     assert element
-    existing_product = drawing.get_assigned_product(element)
-    if existing_product != product:
-        if existing_product:
+    
+    # Get ALL existing products, not just one
+    existing_products = []
+    if hasattr(element, 'HasAssignments'):
+        for rel in element.HasAssignments:
+            if rel.is_a('IfcRelAssignsToProduct'):
+                existing_products.append(rel.RelatingProduct)
+    
+    # Only proceed if the assignment is different
+    if not (len(existing_products) == 1 and existing_products[0] == product):
+        # Unassign from ALL existing products
+        for existing_product in existing_products:
             ifc.run("drawing.unassign_product", relating_product=existing_product, related_object=element)
+        
+        # Assign to the new product
         if product:
             ifc.run("drawing.assign_product", relating_product=product, related_object=element)