Override default max tokens for Anthropic and Groq clients

[danielchalef]

[!IMPORTANT] Override default max tokens for Anthropic and Groq clients, updating __init__ to apply defaults when not provided.

• Override default max tokens for Anthropic and Groq clients.
• Set DEFAULT_MAX_TOKENS to 8192 in anthropic_client.py.
• Set DEFAULT_MAX_TOKENS to 2048 in groq_client.py.
• Update __init__ in AnthropicClient and GroqClient to apply DEFAULT_MAX_TOKENS when config.max_tokens is not provided.

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