0.3.4 - Audio fixes

Two audio fixes for Windows and Android:

• 32X PWM stereo: normal stereo now plays the left and right PWM sources
  independently. Previously, both outputs used the left source. Swapped
  stereo now exchanges the sources correctly.
• YM2612 FM synthesis: algorithms 0, 1, 2, 3, and 5 now retain the
  previous sample's intermediate modulation result, correcting a missing
  delay that affected their sound. Other algorithms and output gain are
  unchanged.

These are targeted fixes, not a claim of fully hardware-accurate audio.
Further work on FM accuracy and mixing remains.

Validation: 92 unit tests and all 13 non-long CTest cases passed. A separate
3,600-frame run with audio enabled passed the existing execution checks,
and the final FM output matched the validated experiment across 3,200,142
stereo sample pairs. Windows and both Android architectures build
successfully; the audio changes have not yet been tested on Android hardware.

The Android APK includes arm64-v8a and x86_64, uses version code 7, and keeps
the same signing certificate as 0.3.3 for in-place updates.

Details: PWM fix,
FM fix,
and FM investigation.

Includes the frame-pacing improvements from 0.3.3 and Android ROM import fix
from 0.3.2. You must supply your own ROM; no ROM or game data is included.