fix: Mark Expr.repeat_by as elementwise (#22068)

Author: coastalwhite

Diff for: crates/polars-ops/src/chunked_array/repeat_by.rs

@@ -11,7 +11,7 @@ type LargeListArray = ListArray<i64>;
 fn check_lengths(length_srs: usize, length_by: usize) -> PolarsResult<()> {
     polars_ensure!(
        (length_srs == length_by) | (length_by == 1) | (length_srs == 1),
-       ComputeError: "repeat_by argument and the Series should have equal length, or at least one of them should have length 1. Series length {}, by length {}",
+       ShapeMismatch: "repeat_by argument and the Series should have equal length, or at least one of them should have length 1. Series length {}, by length {}",
        length_srs, length_by
     );
     Ok(())

Diff for: crates/polars-plan/src/dsl/mod.rs

@@ -1252,7 +1252,7 @@ impl Expr {
 
     #[cfg(feature = "repeat_by")]
     fn repeat_by_impl(self, by: Expr) -> Expr {
-        self.apply_many_private(FunctionExpr::RepeatBy, &[by], false, false)
+        self.map_many_private(FunctionExpr::RepeatBy, &[by], false, None)
     }
 
     #[cfg(feature = "repeat_by")]

Diff for: py-polars/tests/unit/dataframe/test_df.py

@@ -1392,11 +1392,7 @@ def test_repeat_by_unequal_lengths_panic() -> None:
             "a": ["x", "y", "z"],
         }
     )
-    with pytest.raises(
-        ComputeError,
-        match="repeat_by argument and the Series should have equal length, "
-        "or at least one of them should have length 1",
-    ):
+    with pytest.raises(ShapeError):
         df.select(pl.col("a").repeat_by(pl.Series([2, 2])))