Add DeepSeek V4 provider #6339

Job	Run time
build-and-check	3m 4s
test-integration-packages/billing	1m 11s
test-integration-packages/internal	1m 14s
test-integration-packages/agent-runtime	43s
test-integration-sdk	1m 12s
test-integration-cli	40s
test-integration-common	43s
test-integration-web	49s
test-packages/agent-runtime	59s
test-cli	1m 0s
test-common	50s
test-packages/billing	45s
test-web	3m 1s
test-sdk	54s
test-.agents	51s
test-packages/internal	51s
	18m 47s

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