Add DeepSeek V4 provider #6345

Job	Run time
build-and-check	2m 48s
test-integration-packages/internal	1m 13s
test-integration-packages/billing	1m 4s
test-integration-sdk	1m 18s
test-integration-cli	51s
test-integration-common	42s
test-integration-web	41s
test-integration-packages/agent-runtime	49s
test-common	46s
test-.agents	50s
test-packages/agent-runtime	40s
test-packages/billing	42s
test-web	2m 53s
test-cli	1m 2s
test-packages/internal	53s
test-sdk	49s
	18m 1s

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