Refactor STT API (common functions)

[Blaizzy]

We need to refactor our Speech-to-Text (STT) API to extract common functions, eliminate code duplication, and create a more consistent interface across different components.

Requirements

• Identify and extract common functions used across the STT pipeline
• Create a shared utilities module for audio processing functions
• Standardize function signatures and return types
• Separate core functionality from model-specific implementations
• Ensure backward compatibility with existing API consumers
• Improve error handling and logging

[Blaizzy]

Done in #161