Make get_prepared_metadata() public

It is used by cpp-rust-driver

scylla/src/statement/prepared_statement.rs

@@ -397,7 +397,7 @@ impl PreparedStatement {
     }
 
     /// Access metadata about the bind variables of this statement as returned by the database
-    pub(crate) fn get_prepared_metadata(&self) -> &PreparedMetadata {
+    pub fn get_prepared_metadata(&self) -> &PreparedMetadata {
         &self.shared.metadata
     }