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

@@ -34,7 +34,7 @@
 
 #include "iceberg/arrow/arrow_fs_file_io_internal.h"
 #include "iceberg/arrow/arrow_status_internal.h"
-#include "iceberg/arrow/metadata_column_util_internal.h"
+#include "iceberg/arrow_c_data_guard_internal.h"
 #include "iceberg/arrow_c_data_guard_internal.h"
 #include "iceberg/parquet/parquet_data_util_internal.h"
 #include "iceberg/parquet/parquet_register.h"