add PARTITION_SUMMARY_PROP (#2202)

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# Rationale for this change

Adding the snapshot property to keep parity with
[Java](https://github.com/apache/iceberg/commits/main/core/src/main/java/org/apache/iceberg/SnapshotSummary.java)

# Are these changes tested?

Yes I modified two of the existing tests to add this property and added
an additional two for cases where the table is unchanged or
unpartitioned.

# Are there any user-facing changes?

Yes, this will add a property to the Snapshot Summaries when partitions
are changed.

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---------

Co-authored-by: Giorgio Trettenero <gtret@netflix.com>
Co-authored-by: Kevin Liu <kevin.jq.liu@gmail.com>

Author: 3 people

pyiceberg/table/snapshots.py

@@ -58,6 +58,7 @@
 TOTAL_FILE_SIZE = "total-files-size"
 CHANGED_PARTITION_COUNT_PROP = "changed-partition-count"
 CHANGED_PARTITION_PREFIX = "partitions."
+PARTITION_SUMMARY_PROP = "partition-summaries-included"
 OPERATION = "operation"
 
 INITIAL_SEQUENCE_NUMBER = 0
@@ -306,6 +307,8 @@ def build(self) -> Dict[str, str]:
         changed_partitions_size = len(self.partition_metrics)
         set_when_positive(properties, changed_partitions_size, CHANGED_PARTITION_COUNT_PROP)
         if changed_partitions_size <= self.max_changed_partitions_for_summaries:
+            if changed_partitions_size > 0:
+                properties[PARTITION_SUMMARY_PROP] = "true"
             for partition_path, update_metrics_partition in self.partition_metrics.items():
                 if (summary := self._partition_summary(update_metrics_partition)) and len(summary) != 0:
                     properties[CHANGED_PARTITION_PREFIX + partition_path] = summary

tests/table/test_snapshots.py

@@ -224,6 +224,7 @@ def test_snapshot_summary_collector_with_partition() -> None:
         "added-records": "100",
         "deleted-records": "300",
         "changed-partition-count": "2",
+        "partition-summaries-included": "true",
         "partitions.int_field=1": "added-files-size=1234,removed-files-size=1234,added-data-files=1,deleted-data-files=1,added-records=100,deleted-records=100",
         "partitions.int_field=2": "removed-files-size=4321,deleted-data-files=1,deleted-records=200",
     }
@@ -259,11 +260,32 @@ def test_snapshot_summary_collector_with_partition_limit_in_constructor() -> Non
         "added-records": "100",
         "deleted-records": "300",
         "changed-partition-count": "2",
+        "partition-summaries-included": "true",
         "partitions.int_field=1": "added-files-size=1234,removed-files-size=1234,added-data-files=1,deleted-data-files=1,added-records=100,deleted-records=100",
         "partitions.int_field=2": "removed-files-size=4321,deleted-data-files=1,deleted-records=200",
     }
 
 
+@pytest.mark.integration
+def test_partition_summaries_included_not_set_when_no_change() -> None:
+    ssc = SnapshotSummaryCollector()
+    # No files added, so no partition_metrics
+    ssc.set_partition_summary_limit(10)
+    result = ssc.build()
+    assert "partition-summaries-included" not in result
+    assert result == {}  # Should be empty dict
+
+
+@pytest.mark.integration
+def test_partition_summaries_included_not_set_when_unpartitioned_files(table_schema_simple: Schema) -> None:
+    ssc = SnapshotSummaryCollector()
+    data_file = DataFile.from_args(content=DataFileContent.DATA, record_count=100, file_size_in_bytes=1234, partition=Record())
+    ssc.add_file(data_file, schema=table_schema_simple)
+    ssc.set_partition_summary_limit(10)
+    result = ssc.build()
+    assert "partition-summaries-included" not in result
+
+
 def test_merge_snapshot_summaries_empty() -> None:
     assert update_snapshot_summaries(Summary(Operation.APPEND)) == Summary(
         operation=Operation.APPEND,