Naming/contract delta: _root_cfg, _device_boundaries, blocked_coarse_tables; NODE vs EDGE frame

- Coarse/fine name the two members of any pair (Hierarchy docstring); only the
  misleading blocked_base_tables -> blocked_coarse_tables. prepare_fine_boundary
  and blocked_fine_tables keep their pair-relative names.
- Depth-1 static circles use the integer-NODE frame (unchanged behavior); the
  root EDGE frame applies to refined levels only. Contract text corrected.
- _kernel_configs documents why it stays distinct from Hierarchy.configs.
- Drop the stale re-export comment; two tests import table builders from
  refinement_tables. Mechanical caller renames for this delta only.
No numerical code or config derivation changed.

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

tests/validation/multigrid/test_refinement_jets.py

@@ -107,7 +107,7 @@ class JetStepperCPU(unittest.TestCase):
     def test_blocked_amplitude_update_rewrites_only_velocity_column(self):
         backend, htod = mocked([circle()], [jet()], FINE_BLOCKS[1])
         before = backend._fine_tables["surface_velocity"].copy()
-        device = backend._level_boundaries[1].device["surface_velocity"]
+        device = backend._device_boundaries[1].device["surface_velocity"]
         with patch.object(cuda, "memcpy_htod", htod):
             htod.reset_mock()
             backend.set_jet_amplitude(0, -SPEED)