refactor: Clean up and standardize audio store code

Commit notes

This commit refactors the `audio.svelte.ts` file by standardizing the formatting, including consistent use of semicolons and spacing. It also improves the clarity of type definitions and message handling within the audio engine. Additionally, several functions are updated for better readability, and unnecessary comments are removed to streamline the codebase. These changes enhance maintainability and improve overall code quality.