test: update stale fixtures for current sources (no src change)

- test_channel_root: owner is uint64; int() before -1 so the probe slot
  stays an integer under NumPy 1 value-based promotion.
- test_shifted_storage: build FP32 fixtures with FP32 NaN; np.where with a
  Python NaN promoted to FP64 under NumPy 1, so the shifted FP32 contract
  rejected the fixture before the intended checks.
- test_block_stepper: fake backend sets _ddf_shifting (unshifted).
- test_fine_surface_gpu: set _boundary_hosts/_level_jets; fine_boundary
  is now a read-only view over the level lists.
- test_refinement_followup: set _layouts (fine_layout is a read-only
  view); a pair tau that disagrees with its level config is now rejected
  by hierarchy._check_chain before the per-level omega/tau check.

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

tests/validation/multigrid/test_refinement_followup.py

@@ -106,7 +106,7 @@ class FaultGuardsCPU(unittest.TestCase):
 
     def fake_backend(self):
         backend = PeriodicPatchStepper.__new__(PeriodicPatchStepper)
-        backend.fine_layout = None  # dense fine storage
+        backend._layouts = [None, None]  # dense storage on both levels
         backend.ctx = Mock(activate=nullcontext)
         backend._lock = RLock()
         backend._status = "ready"
@@ -158,7 +158,9 @@ class FaultGuardsCPU(unittest.TestCase):
         p = implementation.FixedPatch2D.from_config(cfg, (4, 4, 12, 12))
         with patch.object(cuda, "Stream"), patch.object(implementation.FixedPatch2D, "from_config",
                                                        return_value=replace(p, tau_coarse=.9)):
-            with self.assertRaisesRegex(RuntimeError, "omega/tau"):
+            # The hierarchy rejects a pair tau that disagrees with its level config
+            # (hierarchy.py) before the per-level omega/tau check can be reached.
+            with self.assertRaisesRegex(RuntimeError, "config chain is inconsistent"):
                 PeriodicPatchStepper(cfg, p.bounds, context=context)
         module = Mock()
         module.get_global.return_value = (Mock(), 16)