ggml: backend-agnostic tensor parallelism (experimental) (#19378) #1

Job	Run time
macOS-latest-ios	2m 19s
macOS-latest-visionos	1m 56s
macOS-latest-tvos	2m 45s
macos-latest-ios-xcode	39m 20s
macOS-latest-swift (generic/platform=macOS)	4m 50s
macOS-latest-swift (generic/platform=tvOS)	4m 34s
macOS-latest-swift (generic/platform=iOS)	4m 52s
	1h 0m 36s

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