Proposal: Extracting the public interface files to support iOS integration

[nashysolutions]

Hi,

I have successfully implemented passkeys using this library on my server with a few public interface files removed. My iOS project depends on the public interface files only.

Here is the branch comparison.

Let me know your thoughts.

[nashysolutions]

I have isolated the base64 encoding logic, with some changes. https://github.com/nashysolutions/base64-swift