chore: Move event marshal/unmarshal code to smithy-swift #3342

Job	Run time
linux (5.7-amazonlinux2)	3m 45s
downstream (macos-13-xlarge, Xcode_14.1, platform=iOS Simulator,OS=16.1,name=iPhone 14)	9m 51s
linux (5.7-focal)	3m 39s
downstream (macos-13-xlarge, Xcode_14.1, platform=tvOS Simulator,OS=16.1,name=Apple TV 4K (3rd ge...	6m 44s
linux (5.10-amazonlinux2)	3m 50s
downstream (macos-13-xlarge, Xcode_14.1, platform=OS X)	5m 32s
linux (5.10-jammy)	3m 47s
downstream (macos-14-xlarge, Xcode_15.3, platform=iOS Simulator,OS=17.4,name=iPhone 15)	8m 28s
downstream (macos-14-xlarge, Xcode_15.3, platform=tvOS Simulator,OS=17.4,name=Apple TV 4K (3rd ge...	7m 43s
downstream (macos-14-xlarge, Xcode_15.3, platform=OS X)	7m 40s
	1h 0m 59s

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