chore: clean analyzer to zero issues

Whole-project `flutter analyze` exited 1 on 17 pre-existing info/warning
lints (no errors) in dev tools and test files. Clean them so analyze is
green:
- editor_repository_test: drop the redundant sqflite_common import; keep
  the used utils import with a transitive-dep ignore.
- pen_* widget tests: `(_, __)` wildcard params -> `(_, _)`.
- search_snippet_test / gen_bench_pdf / gen_dense_strokes: drop needless
  interpolation braces; remove an unused `Size` show and an unused local;
  mark the gen tool as print-allowed.

No runtime behavior changed. flutter analyze: No issues found. Affected
tests: 22/22 pass.

tool/gen_bench_pdf.dart

@@ -27,7 +27,7 @@
 
 import 'dart:io';
 import 'dart:math';
-import 'dart:ui' show Offset, Rect, Size;
+import 'dart:ui' show Offset, Rect;
 
 import 'package:flutter_test/flutter_test.dart';
 import 'package:syncfusion_flutter_pdf/pdf.dart';
@@ -207,7 +207,7 @@ void main() {
     final sizeKb = (outFile.lengthSync() / 1024).toStringAsFixed(1);
     print('Generated: $outputPath');
     print('Pages: $pageCount');
-    print('Size: ${sizeKb} KB (${outFile.lengthSync()} bytes)');
+    print('Size: $sizeKb KB (${outFile.lengthSync()} bytes)');
 
     expect(outFile.existsSync(), isTrue);
     expect(outFile.lengthSync(), greaterThan(1024),