Refactor group_by expression handling in DataFrame to use expr_list_to_raw_expr_list for improved clarity and consistency

Author: kosiew

python/datafusion/dataframe.py

@@ -531,18 +531,7 @@ def aggregate(
         group_by_list = group_by if isinstance(group_by, list) else [group_by]
         aggs_list = aggs if isinstance(aggs, list) else [aggs]
 
-        group_by_exprs = []
-        for e in group_by_list:
-            if isinstance(e, str):
-                group_by_exprs.append(Expr.column(e).expr)
-            elif isinstance(e, Expr):
-                group_by_exprs.append(e.expr)
-            else:
-                error = (
-                    "Expected Expr or column name, found:"
-                    f" {type(e).__name__}. Use col() or lit() to construct expressions"
-                )
-                raise TypeError(error)
+        group_by_exprs = expr_list_to_raw_expr_list(group_by_list)
         aggs_exprs = []
         for agg in aggs_list:
             if not isinstance(agg, Expr):