Upgrade CH version to v26.1.2.11

The previous empty-result short-circuit in
``test_random_chain_matches_pandas`` checked
``isinstance(ds_result, pd.DataFrame)``, but ``apply_chain`` returns
a lazy ``DataStore``, not a materialized ``pd.DataFrame`` - so the
isinstance branch was always False and the short-circuit never
fired. CI on commit 64f38b8 surfaced this when Hypothesis generated
the chain ``filter(v>0) -> filter(v>99) -> sort(w desc) ->
groupby(cat).agg({'v':'sum'})`` (empty intermediate after the
second filter; column drift between pandas' agg-projected output
and DataStore's source-bound short-circuit output).

Two changes:

- ``tests/test_property_based_chains.py``: replace the isinstance
  check with a duck-typed ``len(r) == 0`` helper that works on
  ``DataStore`` and ``pd.DataFrame`` alike. Reference the new
  journey test in the comment so future readers can find the
  tracked bug.

- ``tests/journeys/test_property_chain_followups.py`` (new): verbatim
  regression for the falsifying chain, marked
  ``@unittest.expectedFailure``. Follows the
  ``.cursor/rules/chdb-ds.mdc`` rule #6 contract: every Hypothesis
  falsifier becomes a permanent journey test; when the underlying
  empty-intermediate column-projection bug in the executor is
  fixed, flip the xfail and drop the property-test skip in the
  same commit.