Making Queues `Sendable` #160

Job	Run time
unit-tests / macos-unit (macos-13, ~15.2)	3m 59s
unit-tests / macos-unit (macos-14, latest)	2m 20s
unit-tests / api-breakage	6m 9s
unit-tests / linux-unit (swift:5.8-jammy)	2m 50s
unit-tests / linux-unit (swift:5.9-jammy)	3m 15s
unit-tests / linux-unit (swift:5.10-noble)	3m 48s
unit-tests / linux-unit (swiftlang/swift:nightly-6.0-jammy)	4m 31s
unit-tests / linux-unit (swiftlang/swift:nightly-main-jammy)	4m 19s
	31m 11s

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