Add `MultiProducerSingleConsumerChannel` #20

Job	Run time
Test / Windows (5.9 - windows-2022)	7m 47s
Test / macOS (Xcode ${{ matrix.xcode_version }} - ${{ matrix.os_version }} - ${{ matrix.arch }})	0s
Test / Windows (6.0 - windows-2022)	7m 31s
Test / Linux (5.9 - jammy)	56s
Test / Linux (5.10 - jammy)	54s
Test / Windows (6.1 - windows-2022)	8m 1s
Test / Linux (6.0 - jammy)	1m 6s
Test / Windows (nightly - windows-2019)	11m 22s
Test / Linux (6.1 - jammy)	1m 10s
Test / Windows (nightly-6.1 - windows-2019)	10m 32s
Test / Linux (nightly-main - jammy)	1m 31s
Test / Linux (nightly-6.1 - jammy)	1m 26s
Soundness / API breakage check	1m 27s
Soundness / Broken symlinks check	5s
Soundness / Documentation check	1m 14s
Soundness / Format check	41s
Soundness / License headers check	4s
Soundness / Python lint check	5s
Soundness / Shell check	30s
Soundness / Unacceptable language check	3s
Soundness / YAML lint check	5s
	56m 30s

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