[Refactor] Roll out stream helpers to Anthropic Vertex spec (#1094) #3728

Job	Run time
invisible-chars	9s
platform-unit-test (windows-latest)	15m 50s
check-translations	37s
compile	1m 58s
platform-unit-test (ubuntu-latest)	3m 54s
knip	44s
dependency-review	0s
	23m 12s

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