[AMORO-4163][ams] Fix CommitFailedException when loading legacy mixed-iceberg tables on Iceberg 1.7.x

Found while investigating the CI failure in apache#4179.

Iceberg 1.7.x introduced a breaking change in HadoopTableOperations.commit(): it
now uses reference equality (==) to compare the `base` argument against the cached
currentMetadata. Previously, newTableOperations() called ops.current() to obtain the
current metadata, but versionAndMetadata() inside commit() may refresh the internal
state and return a different object instance. When the two references differ, commit()
throws CommitFailedException("Cannot commit changes based on stale table metadata")
even though the metadata content is identical, causing table loading to fail.

Fix: replace ops.current() with ops.refresh() so that the returned TableMetadata
reference is the same object stored in ops' internal cache. When commit() then calls
versionAndMetadata(), it finds the version unchanged on disk and returns the same
cached reference, satisfying the reference-equality check.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: lintingbin

amoro-ams/src/main/java/org/apache/amoro/server/table/internal/InternalMixedIcebergHandler.java

@@ -69,7 +69,12 @@ private TableOperations newTableOperations(boolean changeStore) {
 
       MixedHadoopTableOperations ops =
           new MixedHadoopTableOperations(new Path(tableLocation), io, metaStore.getConfiguration());
-      org.apache.iceberg.TableMetadata current = ops.current();
+      // Use refresh() instead of current() so that the returned TableMetadata reference is the
+      // same object cached inside ops. Iceberg 1.7.x commit() starts with versionAndMetadata()
+      // which compares the `base` argument against the cached reference using == (reference
+      // equality). If current() and versionAndMetadata() return different object instances,
+      // commit() throws CommitFailedException even when the metadata content is identical.
+      org.apache.iceberg.TableMetadata current = ops.refresh();
       if (current == null) {
         return ops;
       }