test: replace duplicated countRows(reader) helper with layout().rowCount()

Both ParquetImporterTest and ParquetImportIntegrationTest reimplemented
the same helper — a full scan decoding every chunk just to sum
rowCount(). VortexReader.layout().rowCount() already answers this
directly from the footer metadata, no scan needed (CsvExporter already
uses it this way for progress tracking).

Author: dfa1

integration/src/test/java/io/github/dfa1/vortex/integration/ParquetImportIntegrationTest.java

@@ -38,14 +38,6 @@ class ParquetImportIntegrationTest {
 
     private static final int EXPECTED_ROWS = 100;
 
-    private static long countRows(VortexReader reader) {
-        var total = new java.util.concurrent.atomic.AtomicLong();
-        try (ScanIterator iter = reader.scan(ScanOptions.all())) {
-            iter.forEachRemaining(c -> total.addAndGet(c.rowCount()));
-        }
-        return total.get();
-    }
-
     private static long countParquetRows(Path path) throws Exception {
         long total = 0;
         try (ParquetFileReader parquet = ParquetFileReader.open(InputFile.of(path));
@@ -106,7 +98,7 @@ void rowCountAndColumnNamesMatch(@TempDir Path tmp) throws Exception {
             DType.Struct schema = (DType.Struct) reader.dtype();
             assertThat(schema.fieldNames().stream().map(io.github.dfa1.vortex.core.model.ColumnName::value).toList()).containsExactlyElementsOf(parquetColumns);
 
-            long vortexRows = countRows(reader);
+            long vortexRows = reader.layout().rowCount();
             assertThat(vortexRows).isEqualTo(EXPECTED_ROWS);
         }
     }
@@ -210,7 +202,7 @@ void parquetAndVortexRowCountsAreEqual(@TempDir Path tmp) throws Exception {
         long parquetRows = countParquetRows(parquetFile);
         long vortexRows;
         try (VortexReader reader = VortexReader.open(vortexFile)) {
-            vortexRows = countRows(reader);
+            vortexRows = reader.layout().rowCount();
         }
         assertThat(vortexRows).isEqualTo(parquetRows);
     }

parquet/src/test/java/io/github/dfa1/vortex/parquet/ParquetImporterTest.java

@@ -23,7 +23,6 @@
 
 import java.nio.file.Path;
 import java.util.List;
-import java.util.concurrent.atomic.AtomicLong;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatThrownBy;
@@ -198,7 +197,7 @@ void importsFixture_schemaAndRowCount(@TempDir Path tmp) throws Exception {
                 assertThat(reader.dtype()).isInstanceOf(DType.Struct.class);
                 DType.Struct schema = (DType.Struct) reader.dtype();
                 assertThat(schema.fieldNames()).contains(ColumnName.of("c_customer_sk"), ColumnName.of("c_first_name"));
-                assertThat(countRows(reader)).isEqualTo(100L);
+                assertThat(reader.layout().rowCount()).isEqualTo(100L);
             }
         }
 
@@ -244,7 +243,7 @@ void projection_importsOnlyRequestedColumns(@TempDir Path tmp) throws Exception
             try (VortexReader reader = VortexReader.open(vortex)) {
                 DType.Struct schema = (DType.Struct) reader.dtype();
                 assertThat(schema.fieldNames()).containsExactly(ColumnName.of("c_customer_sk"));
-                assertThat(countRows(reader)).isEqualTo(100L);
+                assertThat(reader.layout().rowCount()).isEqualTo(100L);
             }
         }
 
@@ -290,12 +289,4 @@ private static Path fixture() throws Exception {
         return Path.of(ParquetImporterTest.class
                 .getResource("/fixtures/delta_encoding_optional_column.parquet").toURI());
     }
-
-    private static long countRows(VortexReader reader) {
-        AtomicLong total = new AtomicLong();
-        try (ScanIterator iter = reader.scan(ScanOptions.all())) {
-            iter.forEachRemaining(c -> total.addAndGet(c.rowCount()));
-        }
-        return total.get();
-    }
 }