feat(neuroml): simplify looking for segment parent's section

The same segment objects are used everywhere, so the segment object in
`parent_seg` will also be the one used in the lists in `ordered_segs`.
So, there's no need to iterate and compare ids, simply look if the
object is in the list.

netpyne/conversion/neuromlFormat.py

@@ -1448,11 +1448,8 @@ def handle_population(
                                         seg.parent.segments
                                     ]
                                     parent_sec = None
-                                    # TODO: optimise
-                                    for sec in ordered_segs.keys():
-                                        if parent_seg.id in [
-                                            s.id for s in ordered_segs[sec]
-                                        ]:
+                                    for sec, segments in ordered_segs:
+                                        if parent_seg in segments:
                                             parent_sec = sec
                                             break