Remove pyg4ometry dependency

[gipert]

At the moment we depend on both Geant4 and pyg4ometry (through reboost), this makes our dependency tree quite complex (and we already see the consequence of this while maintaining the conda-forge feedstock).

Since remage does not need pyg4ometry, let's do the simplest thing: duplicate the few reboost pieces that we need in this package and drop that dependency. I would also not rely on build_hit() at all and just iterate over the output file with LH5Iterator. In the long term we can think about another package but this is not needed now.

[ManuelHu]

I thought more about this. This does not really help for the conda build problem. Even though remage does not require the full reboost and pyg4ometry, the tests very much do so. We run all tests in the conda-forge CI because the reviewer there asked us to do so...

[gipert]

But it's a bit stupid because the user does not need to run the remage tests... maybe we can just remove this part 👼🏻