Fixed staff detection errors

[liebharc]

Fixes some staff detection problems which came up in the smb benchmark.

Disclaimer: Claude code changes which mostly accumulated while I was running it in the background, still have to review this myself

Performance changes

# Start

System level: 5.5 diffs, SER: 4.1%
Polish scores 24.30%
SMB 23.4%

# Staff parsing

System level: 5.6 diffs, SER: 4.7%
Polish scores 21.40%, 42.63%
SMB 19.98%

# Fix NED scoring

Polish scores 19.98%
SMB 16.60%

# Realized that polish ground truth is missing articulations

Polish scores 17.24% 40.23%

It turns out that SMB is also unreliable. For some pieces it omits staccato information which penalizes any model which correctly detect them. I decided to just keep it like that as it's likely not meaningful to spend the time on that.

[weixlu]

Wow, this improvement looks significant!