make from_protobuf and to_protobuf private

Signed-off-by: Richard Chien <[email protected]>

src/common/src/util/sort_util.rs

@@ -38,15 +38,15 @@ pub enum Direction {
 }
 
 impl Direction {
-    pub fn from_protobuf(direction: &PbDirection) -> Self {
+    fn from_protobuf(direction: &PbDirection) -> Self {
         match direction {
             PbDirection::Ascending => Self::Ascending,
             PbDirection::Descending => Self::Descending,
             PbDirection::Unspecified => unreachable!(),
         }
     }
 
-    pub fn to_protobuf(self) -> PbDirection {
+    fn to_protobuf(self) -> PbDirection {
         match self {
             Self::Ascending => PbDirection::Ascending,
             Self::Descending => PbDirection::Descending,
@@ -74,15 +74,15 @@ enum NullsAre {
 }
 
 impl NullsAre {
-    pub fn from_protobuf(nulls_are: &PbNullsAre) -> Self {
+    fn from_protobuf(nulls_are: &PbNullsAre) -> Self {
         match nulls_are {
             PbNullsAre::Largest => Self::Largest,
             PbNullsAre::Smallest => Self::Smallest,
             PbNullsAre::Unspecified => unreachable!(),
         }
     }
 
-    pub fn to_protobuf(self) -> PbNullsAre {
+    fn to_protobuf(self) -> PbNullsAre {
         match self {
             Self::Largest => PbNullsAre::Largest,
             Self::Smallest => PbNullsAre::Smallest,