Fix CI flakiness: data-stream races, QoS inversions, deterministic tests #1673

Job	Run time
Check Protocol	35s
Lint	27s
Build & Test (macos-15, 16.4, macOS,variant=Mac Catalyst)	13m 24s
App Size	4m 25s
Build & Test (xcode-27, latest, visionOS Simulator,name=Apple Vision Pro,OS=27.0)	26m 37s
Build & Test (macos-26, 26.6, macOS, true)	15m 5s
Build & Test (macos-26, 26.6, macOS, true)	14m 1s
Check Changes	5s
Build & Test (macos-26, 26.6, iOS Simulator,name=iPhone 17 Pro,OS=26.5, true)	14m 44s
Build & Test (xcode-27, latest, tvOS Simulator,name=Apple TV 4K (3rd generation),OS=27.0)	10m 14s
Build & Test (macos-26, 26.6, macOS, true)	14m 21s
Build & Test (macos-15, 16.4, tvOS Simulator,name=Apple TV,OS=18.5)	10m 43s
Build & Test (macos-26, 26.6, visionOS Simulator,name=Apple Vision Pro,OS=26.5)	16m 55s
Build & Test (xcode-27, latest, iOS Simulator,name=iPhone 17 Pro,OS=27.0)	13m 39s
Build & Test (macos-26, 26.6, tvOS Simulator,name=Apple TV,OS=26.5)	11m 4s
Build & Test (macos-26, 26.6, iOS Simulator,name=iPhone 17 Pro,OS=26.5, true)	18m 15s
Build & Test (macos-26, 26.6, macOS, true)	14m 28s
Build & Test (xcode-27, latest, macOS,variant=Mac Catalyst)	12m 51s
Build & Test (macos-26, 26.6, macOS,variant=Mac Catalyst)	13m 42s
Build & Test (xcode-27, latest, macOS)	12m 26s
Build & Test (macos-15, 16.4, macOS)	13m 46s
Build & Test (macos-15, 16.4, iOS Simulator,name=iPhone 16 Pro,OS=18.5)	16m 8s
Build Docs	37s
	4h 28m 32s

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