v0.5.4 — Turbo audio dropout fix

What's fixed

Audio no longer drops out under Turbo. Holding Turbo across area and music transitions could silence audio until the next track change (and sometimes not recover). The fix is in the shared APU sound-chip communication: when the game runs faster than real time, commands to the same sound port could collapse together and the sound engine would never see the earlier one. The scheduler now guarantees every distinct command is observed, with no effect on normal-speed timing.

No gameplay or save changes.

ROM not included — provide your own legally-obtained dump.