fix(eval): resolve VitPose image processor metadata

[ssss141414]

Summary

Fixes keypoint-detection evaluation for VitPose checkpoints whose processor metadata names ViTPoseImageProcessor while Transformers exposes VitPoseImageProcessor and cannot resolve the checkpoint through AutoImageProcessor.

This VitPose-family evaluator fix was extracted from #1299 because it is independent of model build, recipes, and Perf.

Changes

• Keep AutoImageProcessor as the primary path.
• Fall back to VitPoseImageProcessor only for the known Unrecognized image processor failure and metadata that identifies the VitPose family.
• Preserve trust_remote_code forwarding.
• Fail early with a clear error when model_id is absent.
• Do not catch unrelated processor errors or alter successful non-VitPose resolution.

Validation

• tests/unit/eval/test_keypoint_detection_evaluator.py: 14 passed
• Ruff check: passed
• Ruff format check: passed
• Previously validated real COCO one-row functional smoke processed one sample and emitted mAP=0.8; this is operability evidence, not an accuracy claim.

Split from #1299.