Support custom model name with "Anthropic" provider

[complyue]

GLM-4.5 supports "Anthropic" api endpoint (and actually works better than OpenAI endpoint), see:

https://docs.z.ai/scenario-example/develop-tools/claude

However, current "Anthropic" provider doesn't support custom model name, in addition to custom base URL which is supported. Even though "OpenAI Compatible" provider is the officially documented way to use GLM-4.5 with Roo Code, and works fine (https://docs.z.ai/scenario-example/develop-tools/roo), consuming GLM-4.5 api via Anthropic api format may give extra advantage to better leverage its optimization around Anthropic working ways.

It's subjectively evidenced by my personal experience using Claude Code in vscode compared to Roo via "OpenAI Compatible", both consuming the same GLM-4.5 api.

I'd like to use GLM-4.5 via "Anthropic" api in Roo.