diagnostics_channel: add BoundedChannel and scopes #4778

Job	Run time
Build slim tarball	2m 14s
aarch64-linux: with shared libraries	19m 15s
aarch64-darwin: with shared libraries	18m 45s
x86_64-darwin: with shared libraries	27m 52s
x86_64-linux: with shared libraries	22m 26s
	1h 30m 32s

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