Local Android audio patch

Based on audioplayers_android 5.3.0 (license retained in LICENSE).

UrlSource duplicates app-owned /proc/self/fd/<fd> sources and passes the descriptor directly to MediaPlayer. Android AppFuse proxies, including remote SAF providers, permit only the original open; reopening the proc path fails. The caller must hold the original lease until source preparation completes. Other URLs and file paths retain upstream behavior.