refactor/rework the unrankable finishers check

[Hiviexd]

current issues:

• very old check and its code is certainly flawed, could really benefit from a revision
• check only works reliably on kantan, futsuu, and muzu difficulties, oni and inner portion really need a rework
• finisher and preceding note same color detection is missing

[hongaaronc]

Sounds good, I'm down to work on this.

Whats unrankable for inners+ though? or is that like an old RC thing that's no longer relevant? Looks like in the old code its saying faster than 1/4 is unrankable for inners, but Ive definitely seen ranked inners with 1/6 + finisher, such as this one:

• wormhole [180 BPM] @ 00:59:956

I can fix up the kantan->oni parts later this week.

[Hiviexd]

for inner it should just shoot up "ensure it makes sense" warnings for 1/3 (or higher) finishers at the start and middle of patterns, and whenever the finisher is the same color as its preceding/next note in 1/3 or higher