Improve unit test coverage

[sashabaranov]

• add tests for config
• add audio tests

[Copilot]

Pull Request Overview

This PR improves unit test coverage by adding tests for configuration behavior and audio processing error scenarios.

• Adds tests for verifying default configuration values and behaviors.
• Introduces multiple error simulation tests for audio API calls using custom failing builders.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
config_test.go	Adds tests for ClientConfig string representation and model mapping behavior.
audio_test.go	Adds tests to simulate and validate error handling in audio API calls.