Feat/note staff schema

[byrongamatos]

🗂️ Migrated PR. Originally opened by @mogul on 2026-06-18 (was #515). Review history not preserved.

Reconstructed from slopsmith/slopsmith#703 — original PR by @zagatozee. Commits replayed with original authorship onto the current main.

Edit schema handling for Piano charts.

Groundwork for importing various chart styles while keeping authored Left Hand and Right Hand information intact. Useful for higher quality piano charts, difficulty options; being able to more accurately turn on or off LH or RH charts at whim while making it so authored information is retained, rather than replacing it with assumed data based on note location.

If "hands cross over" is properly charted (music.xml, Guitar Pro etc) then this should allow that to be accurately depicted in slopsmith piano charts.

Seperate PR on the "https://github.com/slopsmith/slopsmith-plugin-piano/tree/feat/note-staff-schema" branch will follow in due course (ahem, session limited)

Summary by CodeRabbit

• New Features

  • Notes now carry explicit staff-position metadata; serialization and XML/wire formats include this attribute when present.

• Changes

  • Track/drum detection tightened to rely on GPX/General MIDI channel info; older fallback heuristics removed.
  • Drum and bass classification logic updated.
  • Piano/keyboard voice handling refined so voice positions determine staff assignment and LH notes are marked as bass during merging.

[ChrisBeWithYou]

Integration note — from a full-queue dry-run that merged every open org PR into a next-version test build.

song.py and gp2rs.py combine cleanly — the stf/staff field sits alongside main's bend-shape + teaching-mark fields (both additive). The one that needs care is gp2rs_gpx.py: main refactored the GPX left/right-hand piano merge (and GP8 multi-stave folding) into shared helpers _collect_column_notes / _merge_lh_notes, whereas this PR still carries the older inline LH-walk that tags LH notes staff=0.

Fix on rebase: keep main's helper structure and thread the staff value through it — add a staff param to _collect_column_notes and pass staff=0 at the fold sites — rather than reintroducing the inline walk. The main-path RH staff=1/0 assignment auto-merges fine. (Verified: 432 gp2rs/song/notation tests pass with that resolution.)