feat: port demuxer and app to cmake #304

Job	Run time
Lint / Lint	24s
Settings / settings	3s
Build and test / Matrix configuration	6s
Test Linux distros / Matrix configuration	6s
Build docs / Build docs	30s
Official Docker image / Build	36s
Build and test / linux x64 Debug static	15m 50s
Build and test / linux x64 Debug shared	12m 30s
Build and test / linux x64 Release static	16m 43s
Build and test / linux x64 Release shared	16m 36s
Build and test / osx x64 Debug static	20m 21s
Build and test / osx x64 Debug shared	21m 35s
Build and test / osx x64 Release static	25m 24s
Build and test / osx x64 Release shared	43m 16s
Build and test / win x64 Debug static	19m 29s
Build and test / win x64 Debug shared	20m 0s
Build and test / win x64 Release static	32m 30s
Build and test / win x64 Release shared	24m 37s
Build and test / linux arm64 Debug static	19m 56s
Build and test / linux arm64 Debug shared	19m 53s
Build and test / linux arm64 Release static	20m 26s
Build and test / linux arm64 Release shared	20m 25s
Test Linux distros / Alpine	17m 3s
Test Linux distros / ArchLinux	36m 7s
Test Linux distros / CentOS	14m 40s
Test Linux distros / Debian	19m 58s
Test Linux distros / Fedora	17m 49s
Test Linux distros / OpenSUSE	14m 43s
Test Linux distros / Ubuntu	14m 37s
	8h 6m 13s

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