feat(lingbot_va): RoboTwin eef-pose eval, single-file model, Hub checkpoints

Make the LingBot-VA port runnable on both LIBERO and RoboTwin and clean up the
package to LeRobot conventions.

- Consolidate all vendored Wan2.2 model code (transformer, attention, VAE helpers,
  flow-matching scheduler, grid utils, flex-attention) into a single
  modeling_lingbot_va.py; remove the separate wan_*/schedulers modules.
- Move the fixed action (un)normalization quantiles out of the config and into the
  post-processor (LIBERO 7-DoF + RoboTwin 16-d eef); remove the conversion script in
  favour of ready-to-use LeRobot-format checkpoints on the Hub.
- Fixes found via on-sim validation: undo LIBERO's 180-degree image flip
  (image_hflip), encode obs as a multi-frame streaming-VAE clip, reset the streaming
  VAE cache between episodes, run the transformer in config.dtype, lazy-load frozen
  VAE/UMT5 by subfolder with the text encoder on CPU.
- RoboTwin: add an end-effector-pose action mode to RoboTwinEnv (16-d per-arm
  xyz+quat+gripper deltas composed onto the initial eef pose, executed via CuRobo IK)
  and the robotwin_tshape latent layout (full-res head + half-res wrists via a second
  streaming VAE) with the upstream RoboTwin action quantiles + camera mapping.
- Predicted-video saving works for both benchmarks; docs + tests updated.

Co-authored-by: Cursor <cursoragent@cursor.com>

tests/policies/lingbot_va/test_factory.py

@@ -36,17 +36,3 @@ def test_get_policy_class_resolves_lazily() -> None:
     cls = get_policy_class("lingbot_va")
     assert cls.name == "lingbot_va"
     assert cls.config_class is LingBotVAConfig
-
-
-def test_convert_build_config_libero() -> None:
-    pytest.importorskip("diffusers")
-    from lerobot.policies.lingbot_va.convert_lingbot_va_checkpoints import build_config
-
-    cfg = build_config("libero", wan_pretrained_path="dummy/path", dtype="float32")
-    assert cfg.height == 128 and cfg.width == 128
-    assert cfg.used_action_channel_ids == list(range(7))
-    # validate_features (called inside build_config) must have populated the action feature.
-    from lerobot.utils.constants import ACTION
-
-    assert cfg.output_features[ACTION].shape == (7,)
-    assert len(cfg.obs_cam_keys) == 2