* Fix mania editor timestamp generation being culture-dependent
Mostly closes https://github.com/ppy/osu/issues/35809.
* Add failing test for notes with fractions
* Round note time when copying out timestamp & apply half-millisecond tolerance when parsing
Closes the rest of https://github.com/ppy/osu/issues/35809.
One issue here was that while the timestamp generation would allow
fractional object timestamps to be output, the parsing (via
`selection_regex`) would *reject* fractional timestamps, therefore
making lazer incompatible even with itself.
The other is that rounding is probably fine to do anyway for
interoperability with stable. I'd hope nobody actually *needs*
sub-millisecond precision but I'm ready to be proven wrong by some
aspire jokester.
* Specify invariant culture when writing out combo indices to editor timestamp in other rulesets
Pretty sure this is just a much-of-muchness because it's integers but
might as well if I'm spending time here already.