P1 (6/n): exchange-window, raw-exchange, Jet and pinned-remap GPU tests migrated

test_exchange_window, test_raw_exchange_gpu (one fine(block) helper for
the repeated circle+jet construction), test_refinement_jets,
test_multiple_pinned_remap_gpu and test_pinned_body_remap_gpu pass
refinements/level_* lists. Dense fine levels stay level_blocks=[None,
None|block] as before. Assertions unchanged.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/validation/multigrid/test_pinned_body_remap_gpu.py

@@ -25,9 +25,8 @@ B = ((16,16,32,40), (60,16,76,40))
 def make(ctx):
     body = SimObject(71, geometry=CircleGeometry(12.,14.,.8),center=(12.,14.),radius=.8)
     jet = Jet(Tube((10.5,14.),0.,3.,.3),Parallel(0.),'parabolic',.003)
-    run = FixedPatchStepper(CFG,PARENTS,context=ctx,base_block=(4,4),fine_block=(4,4),
-                           child_block=(4,4),child_rectangles_in_parent=A,
-                           child_objects=(body,),child_jets=(jet,))
+    run = FixedPatchStepper(CFG,context=ctx,refinements=[PARENTS,A],level_blocks=[(4,4)]*3,
+                           level_objects=[(),(),(body,)],level_jets=[(),(),(jet,)])
     return run,(body,)