Jets: enforce stationary rule at ObjectManager.set_body_state too

Move the Jet motion check into ObjectManager.validate_jet_motion (uses the
synced field's cut-link jet_id) and call it from both Simulation.set_body
and the direct ObjectManager.set_body_state entry, before any state or
action change. Test both entries, vx too, and that action is untouched.

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

tests/unit/test_jets.py

@@ -243,8 +243,14 @@ def test_set_body_rejects_motion_of_jet_driven_body(device):
     sim = SimpleNamespace(bodies=bodies, field=field, lbm_cfg=field.cfg, _initialized=True)
     with pytest.raises(ValueError, match="stationary"):
         Simulation.set_body(sim, 0, omega=.01)
-    assert bodies.get(0).state.omega == 0
+    with pytest.raises(ValueError, match="stationary"):
+        Simulation.set_body(sim, 0, vx=.01)
+    action = bodies.action.copy()
+    with pytest.raises(ValueError, match="stationary"):
+        bodies.set_body_state(0, omega=.01)  # direct manager entry
+    assert bodies.get(0).state.omega == 0 and np.array_equal(bodies.action, action)
     Simulation.set_body(sim, 0, omega=0.)  # stationary updates stay allowed
+    bodies.set_body_state(0, omega=0.)
 
 
 def test_fine_boundary_keeps_edge_frame_hits_and_checks_jets():