fix: update deprecated Anthropic default model and stop sending both temperature and top_p

[themavik]

Summary

Fixes #392

The AnthropicAgent defaults cause API errors on current Anthropic models:

1. Deprecated model: The default model_id is claude-3-5-sonnet-20240620, which was deprecated in October 2025 and is no longer available.
2. Conflicting parameters: The default_inference_config includes both temperature (0.1) and topP (0.9). Current Anthropic models reject requests that specify both parameters simultaneously.

Changes

• Updated model_id default from claude-3-5-sonnet-20240620 to claude-sonnet-4-20250514
• Removed topP from default_inference_config (keeping only temperature: 0.1)
• Changed _build_input() to only include temperature and top_p in the API request when they have non-None values, so users who explicitly set one or the other still work correctly

Backward Compatibility

• Users who explicitly pass inference_config with their own topP or temperature value will still have those values forwarded to the API -- only the default no longer sends both
• Users who override model_id are unaffected

Test Plan

• Default AnthropicAgent() no longer triggers "model not found" or "cannot set both temperature and top_p" errors
• Explicitly setting inference_config={"topP": 0.9} still works (only top_p sent)
• Explicitly setting inference_config={"temperature": 0.5} still works (only temperature sent)