Build.Step.Options: add comptime_float support

[IOKG04]

It seems to me this was simply forgotten.
Or there is some other reason I neither know nor can observe why this code wouldn't work for comptime_float.

For a more comprehensive fix of/addition to Build.Step.Options, #24057 is the place to look.

[IOKG04]

I should probably provide my usecase for this:
I am coding a pixelart game, and among other things I'm using a pixels_per_unit integer, from which I derive units_per_pixel. With it being 1.0 / 16, an f32 (or even f16) is definitely enough to represent it, but I feel the code would be cleaner if comptime_float would be usable here, as it'd allow changing my main float type to something else without having to also readjust the options.