Fix `base_model_prefix` in the PP-OCR detectors, CLIPSeg, TimesFM, CLIP and VideoPrism heads so base checkpoints load (#48871)
* Fix `base_model_prefix` in the PP-OCR detectors, CLIPSeg, TimesFM, CLIP and VideoPrism heads so base checkpoints load
* Handle tuple entries of MODEL_MAPPING_NAMES in test_base_model_prefix_loads_base_weights
`MODEL_MAPPING_NAMES["funnel"]` is a tuple, so the six Funnel heads were silently skipped by the string comparison; normalise the entry to a tuple of names and test membership.
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Co-authored-by: Raushan Turganbay <raushan@huggingface.co>