KolmogorovSmirnov2Sample: Conditions are ignored

[kklein]

The KolmogorovSmirnov2Sample constraint can be initialized with DataReferences containing Conditions. This is apparent by the parameters in add_ks_2sample_constraint:

https://github.com/Quantco/datajudge/blob/main/src/datajudge/requirements.py#L1276-L1277

Yet, since get_ks_2sample in db_access operates on DataSource objects - instead of DataReference objects - the Conditions attached to DataReferences are ignored.

While a Condition was indeed used in one integration test, it was used for both DataReferences at the same time. Since the same test also succeeds without a Condition it did not became apparent that Conditions are ignored:

https://github.com/Quantco/datajudge/blob/main/tests/integration/test_integration.py#L1768-L1789

Resolving this issue is one of the many things we should obtain for free when tackling #29 and only ever accessing the underlying data via DataReference.get_selection - which takes care of these things under the hood.