[Data] Fix AliasExpr structural equality to respect rename flag (ray-project#60711)

## Description

This PR fixes a bug in AliasExpr.structurally_equals where the rename
marker was always treated as equal, causing incorrect structural
equality results. This could affect logical optimization rules that rely
on accurate expression equivalence (e.g., projection pushdown).


Main changes:
Correct comparison of _is_rename against other._is_rename


## Related issues
> Link related issues: "Fixes ray-project#1234", "Closes ray-project#1234", or "Related to
ray-project#1234".

## Additional information
> Optional: Add implementation details, API changes, usage examples,
screenshots, etc.

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---------

Signed-off-by: slfan1989 <slfan1989@apache.org>
Co-authored-by: Goutam <goutam@anyscale.com>

Author: slfan1989

python/ray/data/expressions.py

@@ -1356,7 +1356,7 @@ def structurally_equals(self, other: Any) -> bool:
             isinstance(other, AliasExpr)
             and self.expr.structurally_equals(other.expr)
             and self.name == other.name
-            and self._is_rename == self._is_rename
+            and self._is_rename == other._is_rename
         )
 
 

python/ray/data/tests/unit/expressions/test_core.py

@@ -259,6 +259,16 @@ def test_alias_structural_equality(self, expr1, expr2, expected):
         """Test structural equality for alias expressions."""
         assert expr1.structurally_equals(expr2) is expected
 
+    def test_alias_structural_equality_respects_rename_flag(self):
+        expr = col("a")
+        aliased = expr.alias("b")
+        renamed = expr._rename("b")
+
+        assert aliased.structurally_equals(aliased)
+        assert renamed.structurally_equals(renamed)
+        assert not aliased.structurally_equals(renamed)
+        assert not aliased.structurally_equals(expr.alias("c"))
+
     def test_alias_evaluation_equivalence(self):
         """Test that alias evaluation produces same result as original."""
         import pandas as pd