perf(library): trim scan ingestion writes

Fresh staging tables hold no path keys, so the first row for an id no longer issues a delete. Removing scanned paths now runs in one transaction with a subselect instead of committing a lookup and two deletes per chunk.

test/sqlite_path_keys_batch_test.dart

@@ -0,0 +1,56 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:spotiflac_android/services/sqlite_helpers.dart';
+import 'package:spotiflac_android/utils/path_match_keys.dart';
+import 'package:sqflite/sqflite.dart';
+
+class _RecordingBatch implements Batch {
+  final operations = <String>[];
+
+  @override
+  void delete(String table, {String? where, List<Object?>? whereArgs}) {
+    operations.add('delete $table ${whereArgs?.single}');
+  }
+
+  @override
+  void insert(
+    String table,
+    Map<String, Object?> values, {
+    String? nullColumnHack,
+    ConflictAlgorithm? conflictAlgorithm,
+  }) {
+    expect(conflictAlgorithm, ConflictAlgorithm.ignore);
+    operations.add('insert $table ${values['item_id']} ${values['path_key']}');
+  }
+
+  @override
+  dynamic noSuchMethod(Invocation invocation) => super.noSuchMethod(invocation);
+}
+
+void main() {
+  const path = '/storage/emulated/0/Music/Album/01 Song.flac';
+
+  test('path keys replace existing rows by default', () {
+    final batch = _RecordingBatch();
+    putPathKeysInBatch(batch, 'stage_keys', 'lib_1', path);
+    expect(batch.operations.first, 'delete stage_keys lib_1');
+    expect(batch.operations.skip(1), [
+      for (final key in buildPathMatchKeys(path))
+        'insert stage_keys lib_1 $key',
+    ]);
+  });
+
+  test('first row in a fresh stage writes the same keys without a delete', () {
+    final batch = _RecordingBatch();
+    putPathKeysInBatch(
+      batch,
+      'stage_keys',
+      'lib_1',
+      path,
+      replaceExisting: false,
+    );
+    expect(batch.operations, [
+      for (final key in buildPathMatchKeys(path))
+        'insert stage_keys lib_1 $key',
+    ]);
+  });
+}