Fix reading EventInfoAux::eventNumber (long long vs int64_t)
RNTuple fixes for reading:
- treat all std::uint64_t fields as 'long long' fields so we can read back EventInfoAux::eventNumber - will discuss with RNTuple devs later
- protect against out of bounds string manipulation in RNTupleReader::init()
- put RNTupleReader into the RootAuxDynIO namespace (NOTE - changes indentation so a lot of lines marked as modified)
This MR should NOT affect normal Athena in any way.