Allow reading Parquet files without explicit projection

Currently, `ParquetReader` requires `ReaderOptions::projection` to be set, otherwise it returns an error. This change allows the reader to infer the schema from the Parquet file metadata if the projection is not provided.

- Modified `src/iceberg/parquet/parquet_reader.cc` to fallback to inferring schema from the file if `projection` is null.
- Added `src/iceberg/test/parquet_reader_no_projection_test.cc` to verify the fix.
- Used `ArrowSchemaGuard` to prevent memory leaks when handling Arrow C schemas.

Co-authored-by: wgtmac <4684607+wgtmac@users.noreply.github.com>

Author: google-labs-jules[bot]

src/iceberg/parquet/parquet_reader.cc

@@ -34,8 +34,8 @@
 
 #include "iceberg/arrow/arrow_fs_file_io_internal.h"
 #include "iceberg/arrow/arrow_status_internal.h"
-#include "iceberg/arrow_c_data_guard_internal.h"
 #include "iceberg/arrow/metadata_column_util_internal.h"
+#include "iceberg/arrow_c_data_guard_internal.h"
 #include "iceberg/parquet/parquet_data_util_internal.h"
 #include "iceberg/parquet/parquet_register.h"
 #include "iceberg/parquet/parquet_schema_util_internal.h"

src/iceberg/test/parquet_reader_no_projection_test.cc

@@ -17,6 +17,8 @@
  * under the License.
  */
 
+#include <arrow/c/bridge.h>
+#include <arrow/json/from_string.h>
 #include <gtest/gtest.h>
 
 #include "iceberg/arrow/arrow_fs_file_io_internal.h"
@@ -26,8 +28,6 @@
 #include "iceberg/schema_internal.h"
 #include "iceberg/test/matchers.h"
 #include "iceberg/type.h"
-#include <arrow/json/from_string.h>
-#include <arrow/c/bridge.h>
 
 namespace iceberg::parquet {
 
@@ -112,8 +112,7 @@ TEST_F(ParquetReaderNoProjectionTest, ReadWithoutProjection) {
 
   // No projection passed
   auto reader_result = ReaderFactoryRegistry::Open(
-      FileFormatType::kParquet,
-      {.path = temp_parquet_file_, .io = file_io_});
+      FileFormatType::kParquet, {.path = temp_parquet_file_, .io = file_io_});
 
   // This is expected to fail currently
   ASSERT_THAT(reader_result, IsOk())