Rounding modes for floating point values differ.

[sigilante]

• ++ff supports 5 rounding modes, default %a.
• ++fl supports 5 rounding modes, default %n.
• ++rh, ++rs, ++rd, ++rq support 4 rounding modes, default %z.
• SoftFloat supports 5 to 6 rounding modes, default softfloat_round_near_even.

Unless there is load-bearing machinery based on these defaults, we should clean these up. This includes changing the default to everywhere be the same and introducing all five rounding modes into all cores.

• https://docs.urbit.org/language/hoon/reference/stdlib/3b