perf(unitree_g1): cap ONNX Runtime thread pool for locomotion policies

Add make_ort_session_options() to build quiet ORT SessionOptions with an
optional CPU thread-pool cap, and load the GR00T balance/walk ONNX policies with
1 intra + 1 inter thread. These small MLPs run at 50 Hz in a background thread;
letting ORT grab every core starves the control loop / torch policy and stutters
the rollout.

src/lerobot/robots/unitree_g1/g1_utils.py

@@ -43,6 +43,24 @@ def get_gravity_orientation(quaternion: list[float] | np.ndarray) -> np.ndarray:
     return gravity_orientation
 
 
+def make_ort_session_options(intra_op_num_threads: int | None = None, inter_op_num_threads: int | None = None):
+    """Build quiet ONNX Runtime SessionOptions, optionally capping the CPU thread pool.
+
+    These tiny MLP policies are latency-bound, not throughput-bound, so letting ORT grab
+    every core starves the real-time control loop / torch policy and causes stutter. Pass
+    1 intra + 1 inter thread for lowest-latency per-step inference.
+    """
+    import onnxruntime as ort
+
+    so = ort.SessionOptions()
+    so.log_severity_level = 3
+    if intra_op_num_threads is not None:
+        so.intra_op_num_threads = intra_op_num_threads
+    if inter_op_num_threads is not None:
+        so.inter_op_num_threads = inter_op_num_threads
+    return so
+
+
 class G1_29_JointArmIndex(IntEnum):
     # Left arm
     kLeftShoulderPitch = 15

src/lerobot/robots/unitree_g1/gr00t_locomotion.py

@@ -68,9 +68,15 @@ def load_groot_policies(
         filename="GR00T-WholeBodyControl-Walk.onnx",
     )
 
-    # Load ONNX policies
-    policy_balance = ort.InferenceSession(balance_path)
-    policy_walk = ort.InferenceSession(walk_path)
+    # Load ONNX policies with a capped thread pool. GR00T runs at 50 Hz in a
+    # background thread alongside the (torch) upper-body policy and IK; letting ORT
+    # grab every core starves those and makes the whole rollout stutter. These are
+    # small MLPs, so 1 thread is both enough and lowest-latency.
+    from .g1_utils import make_ort_session_options
+
+    so = make_ort_session_options(intra_op_num_threads=1, inter_op_num_threads=1)
+    policy_balance = ort.InferenceSession(balance_path, sess_options=so)
+    policy_walk = ort.InferenceSession(walk_path, sess_options=so)
 
     logger.info("GR00T policies loaded successfully")