Fix ruff import order; note resolver statefulness

- Apply ruff I001 import-sorting fix in test file
- Add comment confirming SchemaResolverMjc/Newton/Physx are stateless
  so sharing one proto_resolvers list across proto builders is safe

Author: Horde

source/isaaclab_newton/isaaclab_newton/cloner/newton_replicate.py

@@ -105,6 +105,8 @@ def _build_newton_builder_from_mapping(
     )
 
     # Proto resolvers include SchemaResolverMjc so MjcTendon prims are parsed.
+    # All three resolver classes are stateless (no instance fields); sharing one
+    # set across proto builders is safe.
     proto_resolvers = [SchemaResolverMjc(), SchemaResolverNewton(), SchemaResolverPhysx()]
 
     # The prototype is built from env_0 in absolute world coordinates.

source/isaaclab_newton/test/cloner/test_mjc_tendon_cloner.py

@@ -32,9 +32,8 @@
 import unittest
 
 import newton
-from newton.solvers import SolverMuJoCo
-
 from isaaclab_newton.cloner.newton_replicate import _scope_custom_frequencies
+from newton.solvers import SolverMuJoCo
 
 _TENDON_FREQ = "mujoco:tendon"
 _TENDON_JOINT_FREQ = "mujoco:tendon_joint"
@@ -238,7 +237,11 @@ class TestUsdTendonParsing(unittest.TestCase):
     ROOT = "/robot"
 
     def _build_proto(self, stiffness: float = 1.5) -> newton.ModelBuilder:
-        from newton._src.usd.schemas import SchemaResolverMjc, SchemaResolverNewton, SchemaResolverPhysx  # noqa: PLC0415
+        from newton._src.usd.schemas import (  # noqa: PLC0415
+            SchemaResolverMjc,
+            SchemaResolverNewton,
+            SchemaResolverPhysx,
+        )
 
         stage, _ = _make_minimal_tendon_stage(self.ROOT, stiffness=stiffness)
         b = _mjc_builder()