add get_primary_keys in Schema and add comment at get_primary_keys

Author: XiaoHongbo-Hope

bindings/python/fluss/__init__.pyi

@@ -19,7 +19,7 @@
 
 from enum import IntEnum
 from types import TracebackType
-from typing import Dict, Iterator, List, Optional, Tuple, Union, overload
+from typing import Any, Dict, Iterator, List, Optional, Tuple, Union, overload
 
 import pandas as pd
 import pyarrow as pa
@@ -775,6 +775,7 @@ class Schema:
     def get_column_names(self) -> List[str]: ...
     def get_column_types(self) -> List[str]: ...
     def get_columns(self) -> List[Tuple[str, str]]: ...
+    def get_primary_keys(self) -> List[str]: ...
     def __str__(self) -> str: ...
 
 class TableDescriptor:

bindings/python/src/metadata.rs

@@ -220,6 +220,7 @@ impl Schema {
             .collect()
     }
 
+    /// Get primary key column names, returns empty list if no primary key is defined
     fn get_primary_keys(&self) -> Vec<String> {
         self.__schema
             .primary_key()