feat: update array_to_string function to use pa.string() for delimiter casting

Author: kosiew

python/datafusion/functions.py

@@ -30,6 +30,7 @@
     expr_list_to_raw_expr_list,
     sort_list_to_raw_sort_list,
 )
+from datafusion.types import DataType
 
 if TYPE_CHECKING:
     from datafusion.context import SessionContext
@@ -317,7 +318,7 @@ def decode(expr: Expr, encoding: Expr) -> Expr:
 
 def array_to_string(expr: Expr, delimiter: Expr) -> Expr:
     """Converts each element to its text representation."""
-    return Expr(f.array_to_string(expr.expr, delimiter.cast(str).expr))
+    return Expr(f.array_to_string(expr.expr, delimiter.cast(pa.string()).expr))
 
 
 def array_join(expr: Expr, delimiter: Expr) -> Expr: