Support float step sizes and enforce validation in the set_step method for Number field

[jaakkolehtonen]

• Updated set_step to allow float step sizes
• Added validation to ensure the step size is a positive numeric value, as negative step sizes have no effect in the step attribute of HTML inputs

[jaakkolehtonen]

This change also resolves the PHP 8.1 deprecation notice for implicit conversion from float to int when the passed value is a float.