Function finite_or_none 

pub fn finite_or_none(v: f64) -> Option<f64>

Convert NaN / Infinity to None; finite values to Some(v).

serde_json does not support NaN by default, so any metric that can produce NaN or Infinity (e.g. profit_factor when there are zero losing trades) must go through this before being stored in an Option<f64> report field.