feature: example applications could have settings to set download directory

[davidkoski]

In the example applications, on macOS, we could allow users to select a download directory for the weights. For example they could pick ~/.cache to match the python download directory (though the format may be different)

[johnmai-dev]

HuggingfaceHub matches the Python download directory. It follows the Huggingface cache management standards . The file format remains consistent with huggingface-cli.

SDK Repo: https://github.com/johnmai-dev/HuggingfaceHub

Example: https://github.com/johnmai-dev/ChatMLX/blob/next-1.2.0/Packages/Utilities/Sources/Utilities/Services/HuggingfaceHubService.swift#L14