Fix StepMania Map Conversion

[WilliamQiufeng]

This PR improves the conversion of StepMania maps in the following way:

• Don't repeatedly use addition on floating point numbers to improve precision
• Fix BPM and Stop changes when they are between two rows of notes
• Add SV for stops

[WilliamQiufeng]

I have changed the focus of this PR to improving SM conversion overall. You can test the following maps as an example:

Hatsune Miku's Head Exercises.zip

@Cinammon Roll.zip

PS CodeFactor wants me to put parenthesis in a + b * c. Should I really do that??

[Emik03]

I have changed the focus of this PR to improving SM conversion overall. You can test the following maps as an example:

Hatsune Miku's Head Exercises.zip

@Cinammon Roll.zip

PS CodeFactor wants me to put parenthesis in a + b * c. Should I really do that??

I don't think it's necessary to add parentheses, but I do recommend rearranging it to b * c + a to make it read more organically.