Fix flashlight size multiplier printing with too many decimal digits

[bdach]

Fixes #16750

For understanding why this fixes, see implementation of BindableFloat.

See also, from a distant past:

• Remove all usages of Bindable<float> and Bindable<double> #7709
• Disallow construction of bindables for types that have more specific implementations osu-framework#3229

(above cases are not exactly the same, but as long as BindableFloat exists it should probably be always the instantiated class - there may be value to exposing outwardly as BindableNumber<float> still).