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/unit/test_shifted_storage.py

@@ -78,13 +78,15 @@ class ShiftedStorage(unittest.TestCase):
 
     def test_shifted_density_and_tag_validation(self):
         old,new = topology(A),topology(B)
-        a = tuple(np.where(m[None], np.float32(-.001), np.nan).repeat(9,axis=0) for m in old.leaf_masks)
+        a = tuple(np.where(m[None], np.float32(-.001), np.float32(np.nan)).repeat(9,axis=0)
+                  for m in old.leaf_masks)  # FP32 under numpy 1 and 2 promotion rules
         remap(old,new,a)
         with self.assertRaisesRegex(ValueError,'representation'): remap(old,new,a,False)
         with self.assertRaisesRegex(ValueError,'FP32'): remap(old,new,tuple(x.astype(np.float64) for x in a))
         a[0][:,old.leaf_masks[0]] = -1
         with self.assertRaisesRegex(ValueError,'positive density'): remap(old,new,a)
-        rest = tuple(np.where(m[None],np.float32(0),np.nan).repeat(9,axis=0) for m in old.leaf_masks)
+        rest = tuple(np.where(m[None],np.float32(0),np.float32(np.nan)).repeat(9,axis=0)
+                     for m in old.leaf_masks)
         remap(old,new,rest)
         with self.assertRaisesRegex(ValueError,'positive density'):
             remap_synchronized(old,new,rest,base_count=7,level_steps=(7,14,28),phase='postcollision_g')