feat(audio): add voltex_audio crate with AudioClip type

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

crates/voltex_audio/src/lib.rs

@@ -0,0 +1,7 @@
+pub mod audio_clip;
+pub mod wav;
+pub mod mixing;
+
+pub use audio_clip::AudioClip;
+pub use wav::{parse_wav, generate_wav_bytes};
+pub use mixing::{PlayingSound, mix_sounds};