Fix LIBERO multiview camera resolution

[wayrise]

Summary

LIBERO multiview configs can include target_camera for single-view deployment, but the reader previously treated it as an unconditional override and dropped the wrist stream. This PR resolves cameras from the dataset's advertised features in multiview mode while preserving single-view target-camera behavior.

The reader now supports the canonical image/image2 names and legacy agentview_image/wrist_image / robot0_eye_in_hand_image names, and synchronizes the resolved camera layout used during decoding.

Validation

• Real LIBERO sample: head and wrist tiles decode with nonzero content; only the configured null tile is black.
• pytest -q tests/dataloader/test_libero.py — 8 passed
• pytest -q tests/dataloader tests/benchmarks — 657 passed, 4 skipped (optional labtasker dependency)
• git diff --check — passed