Add daily papers endpoint

[BastienGimbert]

Problem :

There was no simple function to get daily papers by date from the API.

Summary :

Add HfApi.list_daily_papers(date) to call /api/daily_papers.
Add a small test to check the endpoint returns objects and ISO date

Testing

pytest -q tests/test_hf_api.py::PaperApiTest

[HuggingFaceDocBuilderDev]

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