Update cartpole golden images and clean up rendering correctness test

[huidongc]

Description

• Updated golden images due to the content change - upscaling the slider (rail) of the cartpole env
• Committed minor cleanup for the rendering correctness test code: doc, html report, assertion error message, redundant writing of actual image.

Type of change

• Testing

Screenshots

See diff of the golden images.

Checklist

• I have read and understood the contribution guidelines
• I have run the pre-commit checks with ./isaaclab.sh --format
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• I have updated the changelog and the corresponding version in the extension's config/extension.toml file
• I have added my name to the CONTRIBUTORS.md or my name already exists there

[isaaclab-review-bot]

Good cleanup. The docstring fixes are accurate (reset not step), and consolidating the failure path to use the comparison-images directory instead of polluting golden_images/ with timestamped debug artifacts is a clear improvement.

One minor inline comment below — otherwise LGTM.

[greptile-apps]

Greptile Summary

This PR updates 31 cartpole golden-image baselines (across physx/newton backends, isaacsim_rtx/newton_renderer renderers, and various AOVs) following a cartpole slider upscaling change that altered the rendered output. It also includes minor cleanup of test_rendering_correctness.py.

Key changes:

• Updated golden images for all cartpole test combinations (physx + newton backends × rtx + newton renderers × rgb/rgba/depth/albedo/segmentation/simple-shading AOVs), as well as the registered-task golden images for all Cartpole camera task IDs.
• The cartpole pixel-diff threshold remains at 2.0%, which is the tightest threshold in the suite and appropriate for a deterministic cartpole scene.
• Minor test cleanup in test_rendering_correctness.py — the current file state is well-structured with sound logic.

Confidence Score: 5/5

Safe to merge — golden image refresh following a confirmed rendering change, with no logic modifications to the test harness.

All 31 updated golden images are a straightforward refresh caused by the cartpole slider upscaling change. The test file cleanup introduces no new logic. No P0 or P1 issues found.

No files require special attention.

Important Files Changed

Filename	Overview
source/isaaclab_tasks/test/test_rendering_correctness.py	Minor cleanup pass; overall structure and logic are sound. The cartpole pixel-diff threshold (2.0%) is the tightest in the suite and is consistent with a deterministic cartpole scene.
source/isaaclab_tasks/test/golden_images/cartpole/physx-isaacsim_rtx_renderer-rgb.png	Updated golden image baseline following cartpole slider upscaling change.
source/isaaclab_tasks/test/golden_images/registered_tasks/Isaac-Cartpole-RGB-Camera-Direct-v0/default_physics-default_renderer-rgb.png	Updated registered-task golden image baseline for the RGB Cartpole camera task.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A["pytest parametrize\n(physics_backend, renderer, data_type)"] --> B["cartpole_env / shadow_hand_env fixture\nBuilds env with preset overrides\nnum_envs=4, seed=42"]
    B --> C["env.reset()"]
    C --> D["_validate_camera_outputs()"]
    D --> E["For each data_type in sensor output"]
    E --> F["_normalize_tensor() → [0,1] float32"]
    F --> G["_make_grid() → tiled PIL Image"]
    G --> H{"Golden image\nexists?"}
    H -- No --> I["Save as new golden\npytest.fail()"]
    H -- Yes --> J["_compare_images()\npixel L2 norm diff"]
    J --> K{"diff_pct ≤\nthreshold?"}
    K -- Yes --> L["_ssim() score\n(reference only)"]
    K -- No --> M["pytest.fail()"]
    L --> N["Append to _COMPARISON_SCORES"]
    N --> O["Session end:\n_generate_html_report()"]

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