ci, tests : use cmake to download models and remove libcurl dependency (#18791)
* ci, tests : use cmake to download models and remove libcurl dependency
* llama_dl_model -> llama_download_model
* use EXPECTED_HASH for robust model downloading
* Move llama_download_model to cmake/common.cmake
Signed-off-by: Adrien Gallouët <angt@huggingface.co>