[Refactor] Roll out stream helpers to Anthropic Vertex spec #3726

Job	Run time
knip	37s
dependency-review	9s
platform-unit-test (ubuntu-latest)	1m 35s
compile	2m 14s
platform-unit-test (windows-latest)	2m 27s
check-translations	27s
invisible-chars	7s
	7m 36s

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