MP3 Quantization

[Josh200315]

Describe the bug
When exporting as MP3, there is noticeable hitching and general rhythmic inaccuracy in the output file. Upon comparing the MP3 export to live playback from ONBS, it also becomes apparent that the export is a few cents sharp in pitch. The latter is not much of a problem, but the improper quantization is very noticeable in faster (still 10 t/s) songs.

To Reproduce
Steps to reproduce the behavior:

1. Create a note block song with notes in adjacent ticks (for a song whose time signature follows the default bars, this would mean lots of sixteenth notes).
2. Export the song as an MP3 file.
3. Compare the MP3 with live ONBS playback.

Expected behavior
The MP3 export should have the same rhythm and pitch as live ONBS playback.

Additional context
The issue does not seem to be influenced by high concurrent sound counts; the entire MP3 export has the same rhythmic deviation regardless of the number of concurrent sounds (anywhere from about 3 to 85 in this case).

[Bentroen]

This is one of many reasons why the whole MP3 export needs a rework, see #77 and #87.