fix: align Transaction::Apply() with Java BaseTransaction behavior

Match Java's BaseTransaction where hasLastOpCommitted tracks whether
PendingUpdate.commit() was called, not Transaction.commitTransaction().

Key changes:
- Remove last_update_committed_ reversion on Transaction::Commit() failure
- The flag tracks PendingUpdate state (updates applied to metadata_builder_)
- Transaction persistence to catalog is a separate concern

This aligns with Java BaseTransaction.TransactionTableOperations.commit()
at line 645 which sets hasLastOpCommitted=true and never reverts it based
on transaction commit results.

Author: shangxinli

src/iceberg/transaction.cc

@@ -70,8 +70,6 @@ Status Transaction::Apply(std::vector<std::unique_ptr<TableUpdate>> updates) {
   if (auto_commit_) {
     auto result = Commit();
     if (!result.has_value()) {
-      // Commit failed, revert the flag
-      last_update_committed_ = false;
       return std::unexpected(result.error());
     }
   }