fix: remove deprecated downlevelIteration option for TypeScript 6 #4701

Job	Run time
NodeJS installed from stock Ubuntu-LTS packages (not external sources)	1m 30s
build (ubuntu-22.04, 22)	36s
build (ubuntu-22.04, 20)	42s
build (ubuntu-24.04, 22)	39s
build (windows-2025, 18)	43s
build (ubuntu-24.04, 20)	36s
build (windows-2022, 20)	41s
build (windows-2025, 20)	43s
build (windows-2025, 22)	43s
build (ubuntu-22.04, 18)	42s
build (windows-2022, 18)	40s
build (windows-2022, 22)	41s
build (ubuntu-24.04, 18)	40s
Code quality	0s
	9m 36s

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