hardened ParticleData.xml readout against double definition

Both "h0" and "H0" are mapped to the same CORSIKA identifier if you are not careful, so one gets silently overwritten by the other. This MR resolves the issue by raising a RuntimeError if such a situation is encountered, i.e. the build fails.

In the long run we should revisit the enum identifier generation so that such a case does not happen in the first place.

approved this merge request

mentioned in commit f1e4c409

merged

This improvement is very useful and logical. It is clear that "automatic code generation" is in particular very difficult and vulnerable. I still believe it is a great idea, basically we expect that such parts of the code remain extremely stable and are only change in very rare cases.