Mark `{f32,f64}::{next_up,next_down,midpoint}` inline
Most float functions are marked `#[inline]` so any float symbols used by these functions only need to be provided if the function itself is used. RFL recently noticed that `next_up`, `next_down`, and `midpoint` for `f32` and `f64` are not inline, which causes linker errors when building with certain configurations <https://lore.kernel.org/all/20240806150619.192882-1-ojeda@kernel.org/>.
Add the missing attributes so the symbols should no longer be required.
127fbc8481