fix: raise ValueError when all cohorts filtered out in _setup_cohort_queries

Signed-off-by: Suhrid Marwah <suhridmarwah07@gmail.com>

Author: suhr25

malariagen_data/anoph/sample_metadata.py

@@ -1540,6 +1540,12 @@ def _setup_cohort_queries(
             else:
                 cohort_queries_checked[cohort_label] = cohort_query
 
+        if not cohort_queries_checked:
+            raise ValueError(
+                "No cohorts remain after applying the minimum cohort size filter. "
+                "Try reducing `min_cohort_size` or broadening your sample selection."
+            )
+
         return cohort_queries_checked
 
     @_check_types