[SPARK-47906][PYTHON][DOCS] Fix docstring and type hint of hll_union_agg

### What changes were proposed in this pull request?

- Fix docstring;
- Fix type hint: `allowDifferentLgConfigK: Optional[bool]` -> `Optional[Union[bool, Column]]`
- Simplify implementation

### Why are the changes needed?
fix incorrect docstring and type hints

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

### How was this patch tested?
ci

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

Closes #46128 from zhengruifeng/fix_type_hll_union_agg.

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

Author: zhengruifeng

python/pyspark/sql/connect/functions/builtin.py

@@ -3775,16 +3775,14 @@ def hll_sketch_agg(col: "ColumnOrName", lgConfigK: Optional[Union[int, Column]]
 hll_sketch_agg.__doc__ = pysparkfuncs.hll_sketch_agg.__doc__
 
 
-def hll_union_agg(col: "ColumnOrName", allowDifferentLgConfigK: Optional[bool] = None) -> Column:
+def hll_union_agg(
+    col: "ColumnOrName",
+    allowDifferentLgConfigK: Optional[Union[bool, Column]] = None,
+) -> Column:
     if allowDifferentLgConfigK is None:
         return _invoke_function_over_columns("hll_union_agg", col)
     else:
-        _allowDifferentLgConfigK = (
-            lit(allowDifferentLgConfigK)
-            if isinstance(allowDifferentLgConfigK, bool)
-            else allowDifferentLgConfigK
-        )
-        return _invoke_function_over_columns("hll_union_agg", col, _allowDifferentLgConfigK)
+        return _invoke_function_over_columns("hll_union_agg", col, lit(allowDifferentLgConfigK))
 
 
 hll_union_agg.__doc__ = pysparkfuncs.hll_union_agg.__doc__

python/pyspark/sql/functions/builtin.py

@@ -19354,7 +19354,8 @@ def hll_sketch_agg(col: "ColumnOrName", lgConfigK: Optional[Union[int, Column]]
 
 @_try_remote_functions
 def hll_union_agg(
-    col: "ColumnOrName", allowDifferentLgConfigK: Optional[Union[bool, Column]] = None
+    col: "ColumnOrName",
+    allowDifferentLgConfigK: Optional[Union[bool, Column]] = None,
 ) -> Column:
     """
     Aggregate function: returns the updatable binary representation of the Datasketches
@@ -19366,8 +19367,8 @@ def hll_union_agg(
 
     Parameters
     ----------
-    col : :class:`~pyspark.sql.Column` or str or bool
-    allowDifferentLgConfigK : bool, optional
+    col : :class:`~pyspark.sql.Column` or str
+    allowDifferentLgConfigK : :class:`~pyspark.sql.Column` or bool, optional
         Allow sketches with different lgConfigK values to be merged (defaults to false).
 
     Returns
@@ -19412,12 +19413,7 @@ def hll_union_agg(
     if allowDifferentLgConfigK is None:
         return _invoke_function_over_columns("hll_union_agg", col)
     else:
-        _allowDifferentLgConfigK = (
-            lit(allowDifferentLgConfigK)
-            if isinstance(allowDifferentLgConfigK, bool)
-            else allowDifferentLgConfigK
-        )
-        return _invoke_function_over_columns("hll_union_agg", col, _allowDifferentLgConfigK)
+        return _invoke_function_over_columns("hll_union_agg", col, lit(allowDifferentLgConfigK))
 
 
 @_try_remote_functions