Look for gil_scoped_release candidates

Look for parts of the bindings that may benefit from altering the GIL. Note that we have some calls that use `pybind11::call_guard<pybind11::gil_scoped_release>()` [in pyeddl](https://github.com/deephealthproject/pyeddl/blob/1719dfb052394e33148188c559981518e0d21c58/src/eddl_addons.hpp).