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.

test/pen_coordinate_widget_test.dart

@@ -34,7 +34,7 @@ void main() {
               color: const Color(0xFF000000),
               strokeWidth: 0.004,
               onStrokeComplete: committed.add,
-              onEraseStroke: (_, __) {},
+              onEraseStroke: (_, _) {},
             ),
           ),
         ),