fix: test optimizer drops library-level annotations (@Skip, @Tags, @Timeout, ...) #1723

Description

The test optimizer imports every test file and wraps its main() in a plain
group('<path>', () { ... }). Annotations that package:test only reads at the
library level (@Skip, @Tags, @Timeout, @TestOn, @OnPlatform) are
never carried over, so under very_good test / very_good dart test:

• a file marked @Skip(...) runs;
• a file marked @Tags([...]) runs even when dart_test.yaml marks that tag as
  skip:, and -x <tag> / --exclude-tags has no effect on it;
• a file-level @Timeout(...) is ignored and the default 30 seconds applies.

very_good test is the default, optimized path, so a project that relies on
these annotations behaves differently from plain dart test / flutter test
without any warning. The only documented escape hatch is opting the whole file
out of the optimizer with skip_very_good_optimization.

This repository is itself affected: test/ensure_build_test.dart is tagged
pull-request-only (skipped by dart_test.yaml) and carries a 5 minute
@Timeout, yet very_good test -x pull-request-only still runs it with the
default timeout.

Steps To Reproduce

Five files in an empty directory:

# pubspec.yaml
name: optimizer_annotations_repro
environment:
  sdk: ^3.13.0
dev_dependencies:
  test: ^1.31.2

# dart_test.yaml
tags:
  slow:
    skip: "Only run in CI"

// test/fast_test.dart
import 'package:test/test.dart';

void main() {
  test('fast', () => expect(1, 1));
}

// test/slow_test.dart
@Tags(['slow'])

import 'package:test/test.dart';

void main() {
  test('slow', () => expect(1, 1));
}

// test/skipped_test.dart
@Skip('not ready')

import 'package:test/test.dart';

void main() {
  test('skipped', () => fail('must never run'));
}

// test/timeout_test.dart
@Timeout(Duration(milliseconds: 100))

import 'package:test/test.dart';

void main() {
  test('slow to finish', () => Future<void>.delayed(const Duration(seconds: 1)));
}

Then:

dart pub get
dart test            # 1 passed, 2 skipped, 1 failed (the timeout)
dart test -x slow    # same, minus the `slow` suite
very_good dart test  # 3 passed, 1 failed: `slow` and the timed-out test pass, the @Skip file fails

Observed with very_good_cli 1.5.0 on Dart 3.13.2 (macOS):

$ dart test -r expanded
00:00 +0: test/slow_test.dart: (suite)
  Skip: Only run in CI
00:00 +0 ~1: test/skipped_test.dart: (suite)
  Skip: not ready
00:00 +1 ~2 -1: test/timeout_test.dart: slow to finish [E]
  TimeoutException after 0:00:00.100000: Test timed out after 0.1 seconds.
00:00 +1 ~2 -1: Some tests failed.
Failing tests:
  test/timeout_test.dart: slow to finish

$ very_good dart test
00:01 +1: slow to finish            # @Timeout dropped: 1s test passes under the default 30s
00:01 +2: slow                      # @Tags dropped: runs despite dart_test.yaml (and despite -x slow)
skipped test/skipped_test.dart (FAILED)   # @Skip dropped: file ran and hit fail()
00:01 +3 -1: fast
00:01 +3 -1: Some tests failed.
 - test/skipped_test.dart
 	- [FAILED] skipped

Expected Behavior

very_good dart test matches dart test: the @Skip file is skipped, the
slow tag is honoured (skipped by dart_test.yaml, excluded by -x slow),
and the file-level @Timeout fails the 1 second test. Failing that, the
optimizer should at least surface a warning when it drops an annotation, and
the docs should state the limitation next to skip_very_good_optimization.