macOS 15+: FSKit support

[vanyasem]

macOS Sequoia (15+) adds an official API for user-space file systems called FSKit: https://developer.apple.com/documentation/fskit/
Would it be feasible for fuser to support it instead of relying on macFUSE on macOS 15+ targets?

Announcement article: https://eclecticlight.co/2024/06/26/how-file-systems-can-change-in-sequoia-with-fskit/
An example implementation written in Swift: https://github.com/KhaosT/FSKitSample

Apple added FSKit support to Xcode starting with version 16.1 beta
Retail Xcode 16.0 lacks the support for FSKit

That would allow user-space operation on macOS without relying on FUSE-T which was proposed a few times already: #225, #273