[API] fix: anthropic messages API

[AlpinDale]

At some point, the /v1/messages anthropic endpoint broke. This fixes it, and adds the ability to route any request with model name claude-* to the primary loaded model, unless a correct model is provided.

[gemini-code-assist]

Summary of Changes

Hello @AlpinDale, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses a critical issue where the Anthropic /v1/messages API endpoint was non-functional, bringing it back online. Additionally, it introduces a user-friendly feature that allows any request specifying a model name prefixed with claude-* to be automatically directed to the primary loaded model, streamlining the process of interacting with Anthropic-compatible models.

Highlights

• Anthropic Messages API Fix: The pull request resolves a regression that caused the /v1/messages Anthropic endpoint to break, restoring its intended functionality.
• Claude Model Alias Routing: New logic has been introduced to allow model names starting with claude-* to be recognized as aliases and automatically routed to the primary loaded model, enhancing flexibility in model selection.
• Model Name Resolution Overrides: Custom methods (_check_model, _is_model_supported, _get_model_name) were implemented to properly handle and resolve these claude-* aliases during model validation and request processing.
• Streaming Response Refinement: The condition for sending AnthropicContentBlockStop in streaming responses has been adjusted for more accurate and robust termination handling.

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[gemini-code-assist]

Code Review

This pull request aims to fix the Anthropic messages API and introduce a routing mechanism for claude-* model requests. The changes are well-structured and align with the stated objectives. I've identified one critical issue that could lead to a server crash and have provided a detailed comment with a suggested fix to improve the robustness of the implementation.