#[derive(thiserror::Error, Debug)]
pub enum CostError {
#[error("failure reading CSV: {source}")]
CsvIoError {
#[from]
source: csv::Error,
},
#[error("expected state variable name {0} not found in cost rate table")]
StateVariableNotFound(String),
#[error("index {0} for state variable {1} out of bounds, not found in traversal state")]
StateIndexOutOfBounds(usize, String),
}