aarch64-switch-rs's nx crate and code duplication

[XorTroll]

A big part of this project's code (mostly userland IPC client/server code) was copy-pasted from the aforementioned crate and slightly modified, and several types are a direct copy too.

It might be desirable to split the nx crate into several crates, so that one of them just contains plain types in order to avoid code duplication from other projects using them but not wanting/being able to include everything in the full crate, like in this case.