test(D1): exchange, Jet and fine-surface checks run on all-blocked storage

- test_exchange_window and test_raw_exchange_gpu fine(): dense root becomes
  a (12, 8) blocked root (fine(None) stays only for the dense reference test
  that D2 retires);
- jets: G1/G3 compare blocked layouts against the FINE_BLOCKS[0] reference
  (blocked root); the dense run is a separate leg D2 removes; G2 legacy
  actuation vs Jet on the blocked reference; CPU fixtures use a blocked root;
- test_refinement_blocked_fine.raw reads every level through its layout;
- test_fine_surface_gpu: new test_fine_surface_blocked_matches_uniform_four_hops
  (fine ROI after each of four hops vs the uniform 48^2 solver with the same
  tolerances, blowing/suction mass sign from raw exchange, zero actuation ==
  passive bit for bit); the cross-interface donor rejection passes tiles.
  The dense hook/ledger/audit probes in test_fine_surface_four_hops and the
  dense SoA fault tests stay until D2 retires them by name.

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

tests/validation/multigrid/test_exchange_window.py

@@ -109,7 +109,7 @@ class ExchangeWindowGPU(unittest.TestCase):
         from test_raw_exchange_gpu import BOUNDS as RB, CFG, circle as rc, jet, state
         from CelerisLab.cuda.context import CudaContext
         with CudaContext(0) as ctx:
-            kw = dict(context=ctx, refinements=[RB], level_blocks=[None, (16, 20)],
+            kw = dict(context=ctx, refinements=[RB], level_blocks=[(12, 8), (16, 20)],
                       level_objects=[(), (rc(),)], level_jets=[(), (jet(),)],
                       observe_raw_exchange=True)
             with FixedPatchStepper(CFG, observe_window_exchange=True, **kw) as windowed, \