Claude 3: completion_tokens double counting

[adubovik]

Completion tokens are counted twice:

ai-dial-adapter-bedrock/aidial_adapter_bedrock/llm/model/claude/v3/adapter.py

Line 261 in ef2bc40

completion_tokens += usage.output_tokens

ai-dial-adapter-bedrock/aidial_adapter_bedrock/llm/model/claude/v3/adapter.py

Line 274 in ef2bc40

completion_tokens += message.usage.output_tokens

Only one should remain. Preferable one for MessageDeltaEvent.

Add an integration test, e.g. extend the one with max_token=1:

    test_case(
        name="pinocchio in one token",
        max_tokens=1,
        messages=[user("tell me the full story of Pinocchio")],
        expected=lambda s: len(s.content.split()) <= 1
+        and s.usage is not None
+        and s.usage.completion_tokens == 1,
    )