stream: reject duplicate nested transferables #5722

Job	Run time
Build slim tarball	2m 26s
aarch64-darwin: with shared libraries	22m 44s
aarch64-linux: with shared libraries	22m 54s
x86_64-darwin: with shared libraries	27m 47s
x86_64-linux: with shared libraries	26m 49s
	1h 42m 40s

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