add optional range restrictions for numeric CustomFeatureFormat instances

[robfitzgerald]

if a user can overwrite the initial state of charge, they could do so with the wrong unit (ratio vs percent). to avoid this, we could add optional numeric range fields for these types, and use them during encode/decode operations as constraints which can cause StateError responses. for example:

pub enum CustomFeatureFormat {
    FloatingPoint { initial: OrderedFloat<f64>, min: Option<OrderedFloat<f64>>, max: Option<OrderedFloat<f64>> },
    ...
}

impl CustomFeatureFormat {
    pub fn encode_f64(&self, value: &f64) -> Result<StateVar, StateError> {
        match self {
            CustomFeatureFormat::FloatingPoint { initial: _, min, max } => {
                let min_val = min.unwrap_or(OrderedFloat(f64::MIN));
                if value < min_val {
                    Err(...)  // also test vs max
                } else {
                    Ok(StateVar(*value))
                }
            },
            _ => Err(StateError::EncodeError(
                UnitCodecType::FloatingPoint.to_string(),
                self.name(),
            )),
        }
    }
    ...
}

testing this