chore: make Transaction cloneable (#1474)

## What changes are included in this PR?


## Are these changes tested?

No op change, but compilation and existing tests all pass.

Co-authored-by: Renjie Liu <liurenjie2008@gmail.com>

Author: dentiny

crates/iceberg/src/transaction/mod.rs

@@ -74,6 +74,7 @@ use crate::transaction::upgrade_format_version::UpgradeFormatVersionAction;
 use crate::{Catalog, TableCommit, TableRequirement, TableUpdate};
 
 /// Table transaction.
+#[derive(Clone)]
 pub struct Transaction {
     table: Table,
     actions: Vec<BoxedTransactionAction>,
@@ -154,7 +155,7 @@ impl Transaction {
     pub async fn commit(mut self, catalog: &dyn Catalog) -> Result<Table> {
         if self.actions.is_empty() {
             // nothing to commit
-            return Ok(self.table.clone());
+            return Ok(self.table);
         }
 
         self.do_commit(catalog).await