avoid copies of temporal masks

The template argument defining the type of for temporal masks was not
used in the elements/intermediates/metrics functions, and since a copy
from the user-provided input masks is required to not modify it, it
makes more sense to directly initialise it as an xtensor rather than
propagate a template argument to use pytensor/rtensor.

include/evalhyd/detail/determinist/evaluator.hpp

@@ -27,7 +27,7 @@ namespace evalhyd
             const XD2& q_obs;
             const XD2& q_prd;
             // members for optional input data
-            XB3 t_msk;
+            xt::xtensor<bool, 3> t_msk;
             const std::vector<xt::xkeep_slice<int>>& b_exp;
 
             // members for dimensions

include/evalhyd/detail/probabilist/evaluator.hpp

@@ -34,7 +34,7 @@ namespace evalhyd
             const XD2& _q_thr;
             const xt::xtensor<double, 1>& _c_lvl;
             xtl::xoptional<const std::string, bool> _events;
-            XB4 t_msk;
+            xt::xtensor<bool, 4> t_msk;
             const std::vector<xt::xkeep_slice<int>>& b_exp;
 
             // member for "reproducible randomness"