curl --request POST \
  --url https://api.priorlabs.ai/tabpfn/prepare_train_set_upload \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "x_train_info": {
    "filename": "X_train.csv",
    "size_bytes": 1024,
    "content_hash": "abc"
  },
  "y_train_info": {
    "filename": "y_train.csv",
    "size_bytes": 64,
    "content_hash": "def"
  }
}
'

{
  "train_set_upload_id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
  "x_train_info": {
    "signed_urls": [
      "<string>"
    ],
    "expires_at": 123,
    "required_headers": {}
  },
  "y_train_info": {
    "signed_urls": [
      "<string>"
    ],
    "expires_at": 123,
    "required_headers": {}
  }
}