Threading fixes, MAVLink sequence number cleanup #3437

Job	Run time
Ubuntu/Debian packaging (Ubuntu 20.04)	8m 21s
coverage (ubuntu-20.04)	5m 39s
alpine 3.16.0 (musl)	13m 2s
ubuntu-20.04 (package, non-mavsdk_server)	7m 14s
android-arm	6m 18s
ubuntu-22.04 (package, non-mavsdk_server)	6m 14s
linux-armv6	4m 46s
android-arm64	6m 21s
linux-armv6-musl	12m 39s
linux-armv7	4m 51s
android-x86	6m 20s
linux-armv7l-musl	14m 48s
ios	10m 53s
linux-arm64	4m 36s
android-x86_64	6m 27s
linux-arm64-musl	15m 18s
ios_simulator	5m 38s
macOS	7m 48s
ubuntu-22.04 (check style and docs)	6m 9s
ubuntu-20.04 (mavsdk, hunter)	6m 46s
macOS-framework	8m 4s
ubuntu-20.04 (non-mavsdk_server, non-superbuild)	4m 50s
ubuntu-22.04 (proto check)	1m 32s
ubuntu-20.04 (mavsdk_server, superbuild)	12m 54s
Windows	19m 32s
ubuntu-22.04 (mavsdk_server, superbuild)	11m 52s
iOS XCFramework	0s
	3h 38m 52s

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