tests: align closed-owner semantics; route moving-body checks in state regressions

test_failed_moving_step_marks_simulation_failed uses an owner double that
refuses activation after close like CudaContext and expects 'CUDA context
is closed'; test_passive_overlap_failure_keeps_live_state binds the real
moving-body validation methods and a stepper double.

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

tests/unit/test_state_regressions.py

@@ -294,8 +294,11 @@ def test_passive_overlap_failure_keeps_live_state(device, entry, second_x):
     sim = SimpleNamespace(bodies=bodies, field=field, lbm_cfg=field.cfg,
                           _initialized=entry == "runtime_edit",
                           _assert_allocation_contract=lambda: None,
-                          stream=SimpleNamespace(synchronize=device.synchronize))
-    sim._require_usable = Simulation._require_usable.__get__(sim)
+                          stream=SimpleNamespace(synchronize=device.synchronize),
+                          stepper=SimpleNamespace(blocked=None))
+    for name in ("_require_usable", "_moving_bodies", "_reject_moving_bodies",
+                 "_validate_moving_bodies"):
+        setattr(sim, name, getattr(Simulation, name).__get__(sim))
     with pytest.raises(ValueError, match="active fluid receivers|unique cut-link writers"):
         if entry == "sync":
             bodies.sync_to_gpu(field)