Fixed cbm::algo::tof::Hitfind::CalibRawDigis(). Changed interfaces accordingly.

Restored the original functionality of CalibRawDigis(), while keeping the gsl::span implementation.

In order to preserve the possibility of storing the calibrated digis, the return type of cbm::algo::Hitfind() was changed from std::pair to std::tuple. This requires minimal changes of the calling code.

Remark: The cause of the initial bug was confusion which arose from the fact that cbm::algo::Hitfind() modified its input (replacing raw digis by calibrated digis in the input vector), in violation of the single responsibility principle. The calibrated digis are now properly part of the return-type instead, and the input is unchanged.