Penalise the reading difficulty of high velocity notes using "note density"

[buyaspacecube]

Note density refers to how close a note object is to the previous note object, relative to the spacing of base SV 1/4 notes. Pictured below is notes at 1.0 density (top), 0.667 density (middle) and 0.9 with 1.35 mixed in (bottom).

High velocity notes are generally agreed to be easier to read at higher density than lower, making the reading difficulty awarded by some maps with DT unreasonably high. These changes penalise the reading difficulty of high velocity notes at higher densities according to this curve: https://www.desmos.com/calculator/u63f3ntdsi

Some notable SR changes:
XHRONOXAPSULE [HEAVENLY] +DT: 10.36 -> 10.11
Kyouki Chinden [The End] +DT: 10.59 -> 10.37
This Little Girl (Nightcore Amen Edit) [Murder Oni] +DT: 9.87 -> 9.69
No change to SR +HR on any of these maps

[Lawtrohux]

@ppy/pp-maintainers could we please get a smoogisheet for this?

[tsunyoku]

!diffcalc
RULESET=taiko
OSU_A=https://github.com/ppy/osu/tree/pp-dev
OSU_B=#31512

[github-actions]

Target: #31512
Spreadsheet: https://docs.google.com/spreadsheets/d/15tkY70_lNtk3V0_-eVEl2jD12Z26ihs9snH5XIXNcCM/edit

[Lawtrohux]

Looks good to me, reasonable changes that will prevent issues down the line in addition.