Addresses code review feedback about missing automated tests for the ClaudeCodeProvider.
## Changes
- Added unit tests for ClaudeCodeProvider class covering constructor, validateAuth, and getClient methods
- Added unit tests for ClaudeCodeLanguageModel testing lazy loading behavior and error handling
- Added integration tests verifying optional dependency behavior when @anthropic-ai/claude-code is not installed
## Test Coverage
1. **Unit Tests**:
- ClaudeCodeProvider: Basic functionality, no API key requirement, client creation
- ClaudeCodeLanguageModel: Model initialization, lazy loading, error messages, warning generation
2. **Integration Tests**:
- Optional dependency behavior when package is not installed
- Clear error messages for users about missing package
- Provider instantiation works but usage fails gracefully
All tests pass and provide comprehensive coverage for the claude-code provider implementation.
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