Feature Request: Add playback speed (rate) support

[murugandevcare]

Hi 👋,

First of all, thank you for maintaining this library — it’s been really helpful!

I’d like to request a new feature: playback speed (rate) control.

Why?

• Many use cases (e-learning, podcasts, language learning, accessibility, etc.) need the ability to slow down or speed up audio.
• Other audio libraries (e.g., react-native-track-player, expo-av) support this, but it would be great to have it in this lightweight library too.

Suggested API

SoundPlayer.setRate(1.5); // 1.0 = normal, 0.5 = half speed, 2.0 = double speed