feat: async C API and Swift radio state display

Split the dongle session into a fast probe (xone_open) and a background
start (xone_start) that loads the firmware and initializes the radio on
a worker thread, so the app UI never blocks. Add xone_state/xone_error
for progress display, and select the firmware image per product ID when
no path is given. The Swift app polls the state each second and shows
idle/starting/ready/error plus the firmware build or error string.

The session destructor joins the worker so quitting the app does not
terminate on a joinable thread. Note in the CLI and transport that the
recover/re-enumerate path should not be used yet: a crashed SIE drops
off the bus, while the MCU watchdog recovers it after ~90s of quiet.

Co-Authored-By: qwen3.8-27b@q2_k_xl: async C API, Swift state display, and exit-time worker join

CMakeLists.txt

@@ -6,7 +6,7 @@ if(NOT CMAKE_GENERATOR MATCHES "^(Ninja|Xcode)$")
 endif()
 
 cmake_minimum_required(VERSION 3.21)
-project(xone_macos VERSION 0.1.8 LANGUAGES CXX Swift)
+project(xone_macos VERSION 0.1.9 LANGUAGES CXX Swift)
 
 set(CMAKE_EXPORT_COMPILE_COMMANDS ON)