sdk: implement promptAiSdkStream #4019

Job	Run time
build-and-check	2m 33s
test-.agents	31s
test-backend	36s
test-cli	31s
test-common	32s
test-packages/agent-runtime	44s
test-npm-app	36s
test-integration-.agents	42s
test-integration-cli	33s
test-integration-backend	28s
test-web	1m 19s
test-integration-npm-app	31s
test-integration-common	33s
test-integration-web	37s
test-integration-packages/agent-runtime	32s
	11m 18s

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