Make DataStoreObservation properties less lazy #1226
This PR should fix the immediate problem mentioned in #1213, i.e. avoid memory consumption from growing endlessly as more observations are processed. In principle this could mean performance regressions that this change leads to events or IRFs being read from disk more than once. In practice I don't think we do this anywhere, i.e. this change is good.
All tests pass for me locally. Otherwise I didn't test this at all, i.e. I didn't check if it actually solves the memory issue. @adonath - assigning to you.