look over "cargo swift" package for building XCFramework from a Rust library

[heckj]

Highlighted in relatively recent UniFFI documentation: https://github.com/antoniusnaumann/cargo-swift

a cargo plugin to build a Swift Package from Rust code. It provides an init command for setting up a UniFFI crate and a package command for building a Swift package from Rust code - without the need for additional configuration or build scripts.

At a blush from their README, it looks like it provides an interactive UI that does the same steps as what we have in ./scripts/build-xcframework.sh