Threading fixes, MAVLink sequence number cleanup #3438

Job	Run time
Ubuntu/Debian packaging (Ubuntu 20.04)	11m 11s
alpine 3.16.0 (musl)	17m 24s
coverage (ubuntu-20.04)	5m 55s
ubuntu-20.04 (package, non-mavsdk_server)	10m 10s
android-arm	6m 15s
ubuntu-22.04 (package, non-mavsdk_server)	7m 23s
linux-armv6	4m 44s
android-arm64	6m 17s
linux-armv6-musl	11m 59s
android-x86	6m 22s
linux-armv7	6m 24s
linux-armv7l-musl	17m 13s
ios	8m 56s
android-x86_64	8m 38s
linux-arm64	4m 52s
linux-arm64-musl	17m 26s
ios_simulator	6m 13s
macOS	8m 3s
ubuntu-20.04 (mavsdk, hunter)	4m 43s
macOS-framework	15m 22s
ubuntu-20.04 (non-mavsdk_server, non-superbuild)	4m 45s
ubuntu-22.04 (check style and docs)	7m 41s
ubuntu-22.04 (proto check)	1m 34s
ubuntu-20.04 (mavsdk_server, superbuild)	10m 20s
Windows	14m 3s
ubuntu-22.04 (mavsdk_server, superbuild)	12m 52s
iOS XCFramework	59s
	3h 57m 44s

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