Implement Anthropic Provider

[LittleCoinCoin]

Description:
Implement Anthropic Claude API provider.

Acceptance Criteria:

• Anthropic provider implemented with Claude models
• Tool calling functionality adapted to Anthropic's format (MCP, so I hope it won't be too hard...)
• Authentication working with Anthropic API keys
• Response format standardization matching the abstraction layer

Dependencies:

• Requires Issue LLM Provider Abstraction Layer #16