fn counts_add_assign<K, V>(lhs: &mut EnumMap<K, V>, rhs: EnumMap<K, V>)
where
    K: EnumArray<V>,
    V: AddAssign,
{
    for (k, v) in rhs {
        lhs[k] += v;
    }
}
Combines two `HashMap`s together. If a key is in both maps, the values are added together.
crates/core/executor/src/report.rs