[MINOR][PYTHON][DOCS] Refine the examples in window.py

### What changes were proposed in this pull request?
Refine the examples in window.py

### Why are the changes needed?
use the recommended way to import functions

### Does this PR introduce _any_ user-facing change?
yes, doc-only changes

### How was this patch tested?
CI

### Was this patch authored or co-authored using generative AI tooling?
No

Closes apache#53112 from zhengruifeng/doc_win_fun_import.

Authored-by: Ruifeng Zheng <ruifengz@apache.org>
Signed-off-by: Ruifeng Zheng <ruifengz@apache.org>

Author: zhengruifeng

python/pyspark/sql/window.py

@@ -86,8 +86,7 @@ def partitionBy(*cols: Union["ColumnOrName", Sequence["ColumnOrName"]]) -> "Wind
 
         Examples
         --------
-        >>> from pyspark.sql import Window
-        >>> from pyspark.sql.functions import row_number
+        >>> from pyspark.sql import Window, functions as sf
         >>> df = spark.createDataFrame(
         ...      [(1, "a"), (1, "a"), (2, "a"), (1, "b"), (2, "b"), (3, "b")], ["id", "category"])
         >>> df.show()
@@ -105,7 +104,7 @@ def partitionBy(*cols: Union["ColumnOrName", Sequence["ColumnOrName"]]) -> "Wind
         Show row number order by ``id`` in partition ``category``.
 
         >>> window = Window.partitionBy("category").orderBy("id")
-        >>> df.withColumn("row_number", row_number().over(window)).show()
+        >>> df.withColumn("row_number", sf.row_number().over(window)).show()
         +---+--------+----------+
         | id|category|row_number|
         +---+--------+----------+
@@ -139,8 +138,7 @@ def orderBy(*cols: Union["ColumnOrName", Sequence["ColumnOrName"]]) -> "WindowSp
 
         Examples
         --------
-        >>> from pyspark.sql import Window
-        >>> from pyspark.sql.functions import row_number
+        >>> from pyspark.sql import Window, functions as sf
         >>> df = spark.createDataFrame(
         ...      [(1, "a"), (1, "a"), (2, "a"), (1, "b"), (2, "b"), (3, "b")], ["id", "category"])
         >>> df.show()
@@ -158,7 +156,7 @@ def orderBy(*cols: Union["ColumnOrName", Sequence["ColumnOrName"]]) -> "WindowSp
         Show row number order by ``category`` in partition ``id``.
 
         >>> window = Window.partitionBy("id").orderBy("category")
-        >>> df.withColumn("row_number", row_number().over(window)).show()
+        >>> df.withColumn("row_number", sf.row_number().over(window)).show()
         +---+--------+----------+
         | id|category|row_number|
         +---+--------+----------+
@@ -214,8 +212,7 @@ def rowsBetween(start: int, end: int) -> "WindowSpec":
 
         Examples
         --------
-        >>> from pyspark.sql import Window
-        >>> from pyspark.sql import functions as func
+        >>> from pyspark.sql import Window, functions as sf
         >>> df = spark.createDataFrame(
         ...      [(1, "a"), (1, "a"), (2, "a"), (1, "b"), (2, "b"), (3, "b")], ["id", "category"])
         >>> df.show()
@@ -234,7 +231,7 @@ def rowsBetween(start: int, end: int) -> "WindowSpec":
         in partition ``category``
 
         >>> window = Window.partitionBy("category").orderBy("id").rowsBetween(Window.currentRow, 1)
-        >>> df.withColumn("sum", func.sum("id").over(window)).sort("id", "category", "sum").show()
+        >>> df.withColumn("sum", sf.sum("id").over(window)).sort("id", "category", "sum").show()
         +---+--------+---+
         | id|category|sum|
         +---+--------+---+
@@ -294,8 +291,7 @@ def rangeBetween(start: int, end: int) -> "WindowSpec":
 
         Examples
         --------
-        >>> from pyspark.sql import Window
-        >>> from pyspark.sql import functions as func
+        >>> from pyspark.sql import Window, functions as sf
         >>> df = spark.createDataFrame(
         ...      [(1, "a"), (1, "a"), (2, "a"), (1, "b"), (2, "b"), (3, "b")], ["id", "category"])
         >>> df.show()
@@ -314,7 +310,7 @@ def rangeBetween(start: int, end: int) -> "WindowSpec":
         in partition ``category``
 
         >>> window = Window.partitionBy("category").orderBy("id").rangeBetween(Window.currentRow, 1)
-        >>> df.withColumn("sum", func.sum("id").over(window)).sort("id", "category").show()
+        >>> df.withColumn("sum", sf.sum("id").over(window)).sort("id", "category").show()
         +---+--------+---+
         | id|category|sum|
         +---+--------+---+