minValue static method
Creates a validation rule that enforces a minimum numeric value.
Returns an error message if the value is less than min.
If message is not provided, uses a default message.
Example:
Validations.minValue(0, 'Value must be positive')
Implementation
static String Function(double?) minValue(double min, [String? message]) {
return (double? value) => (value ?? double.negativeInfinity) < min ? message ?? 'Value must be at least $min' : '';
}