feat(audio): add experimental MP3 on-demand range decoder

Adds mp3_open/mp3_decode_range/mp3_close API backed by miniaudio
ma_decoder for in-memory MP3 assets. Guarded by #if !defined(STRIP_ALL);
any use in stripped builds is a compile error. No new dependencies:
drmp3 is already compiled via MINIAUDIO_IMPLEMENTATION in audio.cc.

handoff(Gemini): mp3_sample.{h,cc} in AUDIO_SOURCES. Usage:
  Mp3Decoder* d = mp3_open(GetAsset(id, &sz), sz);
  mp3_decode_range(d, start_frame, num_frames, pcm_out);
  mp3_close(d);

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

0 files changed, 0 insertions, 0 deletions