Fix slider calculation for evenly divisible values

[StefanSlehta]

When using the slider, I noticed a bug where for evenly divisible values, the slider doesn't step correctly.

Example, for

  SliderSettingsTile(
              settingKey: 'my-key',
              title: 'Slider demo',
              defaultValue: 100.0,
              minValue: 0.0,
              maxValue: 100.0,
              step: 10.0,
            ),

I get the following result

Likely because 100 / 10 + 1 = 11, so the step becomes 100 / 11 = 9.090909...

After the fix, for the same code

Sorry for the super slow gif, conversion from mov wasn't the best.