…truncated tracks

- SectorReader.ParseTracksWithLba: stop adding Pregap frames to
  ChdOffset/StartLba. chdman stores the pregap inside the track's
  FRAMES (silence before the data), so the old offsets shifted every
  track after the first pregap by 150 frames (2s) — music started
  late, each track's tail bled into the next track's intro, and the
  last track mapped past the CHD end, leaving its final 148 frames
  unreadable (declared BIN/WAV sizes exceeded the readable content).

- ChdContainer virtual export:
  * CUE/ISO mode: the .iso now contains the audio tracks the CUE
    references (audio sectors at 2352 B/s), so emulators no longer hit
    EOF on CD audio reads; the declared size now matches the content.
  * WAV export: skip the pregap frames so each WAV begins at the
    music (INDEX 01 00:00:00) and has the correct length
    ((frames - pregap) * 2352).
  * ReadVirtualBin/ReadVirtualWav use the per-track sector size and
    pregap-aware offsets consistently.

…truncated tracks

- SectorReader.ParseTracksWithLba: stop adding Pregap frames to
  ChdOffset/StartLba. chdman stores the pregap inside the track's
  FRAMES (silence before the data), so the old offsets shifted every
  track after the first pregap by 150 frames (2s) — music started
  late, each track's tail bled into the next track's intro, and the
  last track mapped past the CHD end, leaving its final 148 frames
  unreadable (declared BIN/WAV sizes exceeded the readable content).

- ChdContainer virtual export:
  * CUE/ISO mode: the .iso now contains the audio tracks the CUE
    references (audio sectors at 2352 B/s), so emulators no longer hit
    EOF on CD audio reads; the declared size now matches the content.
  * WAV export: skip the pregap frames so each WAV begins at the
    music (INDEX 01 00:00:00) and has the correct length
    ((frames - pregap) * 2352).
  * WAV-mode data-track INDEX positions are now relative to the
    data-file content instead of the cumulative disc frame stream, so
    audio-first layouts and multiple data tracks produce correct CUE
    sheets.
  * Single-file (non-WAV) modes now register the BIN/ISO entry even
    for audio-only discs, which the CUE references but which was
    previously missing from the mount.
  * Audio sectors in BINARY files use 2352 B/s only when the CHD
    stores raw sectors (UnitBytes >= 2352); cooked 2048-byte-unit
    CHDs (theoretical; chdman cannot produce them with audio) read at
    the unit size.
  * ReadVirtualBin/ReadVirtualWav use the per-track sector size and
    pregap-aware offsets consistently.
```