amend bootstrap algorithm to support more than just daily predictions

At the moment, there is a check on the length of each year block, but there is an assumption that predictions are daily:

// check that year is complete (without a rigorous leap year check)
int n_days = xt::sum(wdw)();
if ((n_days != 365) && (n_days != 366))
{
    throw std::runtime_error(
        "year starting in " + std::to_string(y - 400)
        + " is incomplete"
    );
}

https://gitlab.irstea.fr/HYCAR-Hydro/evalhyd/evalhyd-cpp/-/blob/805e4a6af9271dec04e55417d7539b7c09841f40/include/evalhyd/detail/uncertainty.hpp#L107-115

This check needs to be made more versatile so that another temporal resolution can be considered, as long as complete years are provided.