fix(downloads): use certifi for robust SSL certificate verification

[aoulaa]

fix(downloads): use certifi for robust SSL certificate verification

Description

This change updates the SSL context creation in `download_utils.py` to explicitly use the `certifi` CA bundle. This ensures that the application has access to a reliable, up-to-date set of root certificates, which is critical for verifying SSL connections to external services like Hugging Face.

Problem

On macOS environments (and potentially others), Python's default SSL context often fails to locate the system's root certificates. This leads to `aiohttp.client_exceptions.ClientConnectorCertificateError` errors when attempting to download models.

Solution

By passing `cafile=certifi.where()` to `ssl.create_default_context()`, we force the application to use the trusted certificate store provided by the `certifi` package. This is a standard best practice for cross-platform Python applications and resolves the verification failure.