Support for Swift package manager

[basoppenheim]

Adds Swift Package Manager support by introducing a Package.swift manifest for the existing macOS library.

Scope:

• No intended behavior change to the library itself
• Keeps the package macOS-only, matching the current IOKit-based implementation
• Makes the library easier to consume in modern Xcode/SPM-based projects

[basoppenheim]

I cleaned up the commit history to make it a single commit.

I appreciate this project for enabling users who aren't on macOS 13+ (when Apple added native Joy-Con support) to use Joy-Cons. I've been using my fork for the last 3 years, so the changes are well-tested at this point. Would love to see this merged if you're still open to it.