Apply suggestion from @AndreasAlbertQC

Author: AndreasAlbertQC

dataframely/schema.py

@@ -816,7 +816,13 @@ def cast(
 
         def _cast_to_schema(
             lf: pl.LazyFrame, schema: dict[str, pl.DataType]
-        ) -> pl.LazyFrame:
+        # NOTE: This function does almost the same thing as `match_to_schema`, except:
+        #
+        # 1. It raises a polars `polars.exceptionsColumnNotFoundError` on missing columns, 
+        #    while `match_to_schema` raises a `dataframely.exc.SchemaError`
+        # 2. The error is raised only at collection time, while `match_to_schema` raises immediately
+        #
+        # This behavior is needed to not break backward compatibility.
             return lf.select(cls.column_names()).cast(
                 {
                     name: col.dtype