ISF remove un-needed const to avoid const_cast

ISF remove un-needed const to avoid const_cast

Basically if we actually do what @jchapman said in !58205 (merged)

Conceptually we would consider the whole GenEvent including all GenParticle objects as non-const during simulation

We do not need to const_cast. But the relevant interfaces were actually written the other way wrt to @jchapman comment. So we need to rm quite a few const

ping @fwinkl and @jchapman , the ISF Services seem to now pass the checker ... I compiled the full Simulation/ISF/.* also with HepMC3 but lets wait for CI there might be still const somewhere ...