stream: reject duplicate nested transferables #5634

Job	Run time
Build slim tarball	1m 47s
x86_64-darwin: with shared libraries	33m 14s
aarch64-linux: with shared libraries	18m 34s
aarch64-darwin: with shared libraries	17m 33s
x86_64-linux: with shared libraries	21m 11s
	1h 32m 19s

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