Expose NRG sessions, tracks and raw CD-DA extraction

[Hawkynt]

What changed

• expose NRG session/track topology from NrgReader instead of collapsing the container to one ISO track
• parse per-session CUEX + DAOX/DAOI metadata and TAO ETN2/ETNF tracks, including track numbers, mode, sector geometry, pregap/data byte ranges, index LBAs, ADR/control, MCN and ISRC
• expose raw CDTX pack bytes
• probe ISO 9660 independently on every data track
• preserve the first ISO filesystem at the archive root for compatibility; namespace later ISO filesystems below .nrg/session-XX/track-YY/iso
• expose CD-DA and non-ISO data tracks as exact raw .bin archive entries below .nrg/session-XX/tracks
• add ExtractTrack / CopyTrackTo so large tracks can be copied without transcoding; 2352/2448-byte CD-DA sector representations are preserved exactly
• tighten rebuild maintenance so a single non-ISO data track cannot be flattened into a new ISO image

Compatibility

Existing single-ISO NRG callers still see their ISO files at the archive root. The richer topology is additive through Sessions / Tracks; synthetic raw-track entries only appear for content not represented by a readable ISO tree.

References / licensing

NRG remains proprietary with no public normative Nero specification. The implementation uses reverse-engineered public format facts and behavioral oracles only. CDEmu/libMirage is GPL and is not copied or translated; this remains a clean-room managed C# implementation. The DAO/CUE layouts were cross-checked against independently documented NRG structures and public CD image tooling.

Tests

Added coverage for mixed-mode topology, MCN/ISRC/CD-TEXT, raw CD-DA extraction, 2448-byte subchannel preservation, pregap streaming, multiple ISO sessions, non-ISO raw data tracks, and maintenance refusal for a raw single-track data image.