Core ML: fix the output contract, the model never loaded through the task

Core ML: replace the int8 variant with fp16

Update models

Add spec-compliant config.json files

Add spec-compliant config.json files

Restructure to MODEL_SPEC.md convention

Delete coreml/config.json

Upload rfdetr_n_seg_coreml_int8.pte

Create coreml/config.json