`bevy_core_widgets` slider precision rounding issues

## Bevy version and features

`eed2e0ebe`

## \[Optional\] Relevant system information
`rustc 1.91.0-nightly (523d3999d 2025-08-30)`
`6.12.44 x86_64` `12th Gen Intel i5-12600K`

## What went wrong
negative exponents in `SliderPrecision` result in inaccurate numbers (e.g. 3999.999998 instead of 4000).
This can be fixed by multiplying by the reciprocal instead of dividing by the factor again, but then the same issue appears for positive exponents (e.g. 5.319999996 instead of 5.32).
```rust
fn round(&self, value: f32) -> f32 {
let factor = ops::powf(10.0_f32, self.0 as f32);
let rounded = (value * factor).round();
if self.0.is_positive() {
rounded / factor
} else {
let recip = ops::powf(10.0_f32, -self.0 as f32);
rounded * recip
}
}
```
this results in the right apparent numbers for both positive and negative exponents, but I'm not sure if this is in any way dependent on my machine/rustc/libm.