fix: add primary keys to stats tables to prevent ctid-based update conflicts

When using PostgreSQL as the metadata catalog with multiple concurrent
writers (e.g., Kafka Connect tasks), UPDATE statements on tables without
primary keys cause postgres_scanner to use ctid (physical row ID) for
row identification. This leads to serialization failures because ctid
changes when rows are updated due to PostgreSQL's MVCC.

Changes:
- Add PRIMARY KEY to ducklake_table_stats on table_id
- Add composite PRIMARY KEY to ducklake_table_column_stats on (table_id, column_id)

This allows postgres_scanner to use logical key-based updates instead of
ctid-based updates, eliminating "could not serialize access due to
concurrent update" errors under high concurrency.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: fuziontech

src/storage/ducklake_metadata_manager.cpp

@@ -73,8 +73,8 @@ CREATE TABLE {METADATA_CATALOG}.ducklake_data_file(data_file_id BIGINT PRIMARY K
 CREATE TABLE {METADATA_CATALOG}.ducklake_file_column_stats(data_file_id BIGINT, table_id BIGINT, column_id BIGINT, column_size_bytes BIGINT, value_count BIGINT, null_count BIGINT, min_value VARCHAR, max_value VARCHAR, contains_nan BOOLEAN, extra_stats VARCHAR);
 CREATE TABLE {METADATA_CATALOG}.ducklake_delete_file(delete_file_id BIGINT PRIMARY KEY, table_id BIGINT, begin_snapshot BIGINT, end_snapshot BIGINT, data_file_id BIGINT, path VARCHAR, path_is_relative BOOLEAN, format VARCHAR, delete_count BIGINT, file_size_bytes BIGINT, footer_size BIGINT, encryption_key VARCHAR);
 CREATE TABLE {METADATA_CATALOG}.ducklake_column(column_id BIGINT, begin_snapshot BIGINT, end_snapshot BIGINT, table_id BIGINT, column_order BIGINT, column_name VARCHAR, column_type VARCHAR, initial_default VARCHAR, default_value VARCHAR, nulls_allowed BOOLEAN, parent_column BIGINT, default_value_type VARCHAR, default_value_dialect VARCHAR);
-CREATE TABLE {METADATA_CATALOG}.ducklake_table_stats(table_id BIGINT, record_count BIGINT, next_row_id BIGINT, file_size_bytes BIGINT);
-CREATE TABLE {METADATA_CATALOG}.ducklake_table_column_stats(table_id BIGINT, column_id BIGINT, contains_null BOOLEAN, contains_nan BOOLEAN, min_value VARCHAR, max_value VARCHAR, extra_stats VARCHAR);
+CREATE TABLE {METADATA_CATALOG}.ducklake_table_stats(table_id BIGINT PRIMARY KEY, record_count BIGINT, next_row_id BIGINT, file_size_bytes BIGINT);
+CREATE TABLE {METADATA_CATALOG}.ducklake_table_column_stats(table_id BIGINT, column_id BIGINT, contains_null BOOLEAN, contains_nan BOOLEAN, min_value VARCHAR, max_value VARCHAR, extra_stats VARCHAR, PRIMARY KEY (table_id, column_id));
 CREATE TABLE {METADATA_CATALOG}.ducklake_partition_info(partition_id BIGINT, table_id BIGINT, begin_snapshot BIGINT, end_snapshot BIGINT);
 CREATE TABLE {METADATA_CATALOG}.ducklake_partition_column(partition_id BIGINT, table_id BIGINT, partition_key_index BIGINT, column_id BIGINT, transform VARCHAR);
 CREATE TABLE {METADATA_CATALOG}.ducklake_file_partition_value(data_file_id BIGINT, table_id BIGINT, partition_key_index BIGINT, partition_value VARCHAR);