Add `MultiProducerSingleConsumerChannel` #6

Job	Run time
Test / Windows (5.9 - windows-2022)	13m 1s
Test / Linux (5.8 - jammy)	44s
Test / Windows (6.0 - windows-2022)	18m 47s
Test / Linux (5.9 - jammy)	46s
Test / Windows (nightly - windows-2019)	10m 48s
Test / Linux (5.10 - jammy)	47s
Test / Windows (nightly-6.1 - windows-2019)	10m 35s
Test / Linux (6.0 - jammy)	54s
Test / Linux (nightly-main - jammy)	1m 24s
Test / Linux (nightly-6.1 - jammy)	1m 22s
Soundness / Documentation check	1m 3s
Soundness / Broken symlinks check	5s
Soundness / API breakage check	54s
Soundness / Format check	35s
Soundness / License headers check	4s
Soundness / Python lint check	7s
Soundness / Shell check	36s
Soundness / Unacceptable language check	4s
Soundness / YAML lint check	5s
	1h 2m 41s

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