Native Anthropic Chat Completion Support

Use Anthropic models natively in the inference service with full chat_completion support.

**What the feature is**
Native chat_completion task type support for Anthropic in the inference service, including streaming, tool handling, and system prompt formatting.

**Who bis this feature for**
Developers building conversational applications who want to use their own Anthropic API keys.

**Expected outcome**
Without native support, customers have to route Anthropic requests through external services, adding latency and infrastructure overhead. Native support cuts that out, so teams can stream responses and use advanced model features like tool handling and system prompts directly.

**Key user stories / use cases**
Streaming conversational responses from Anthropic models, using tool handling and system prompts natively, and simplifying infrastructure for teams already on Anthropic.