feat(deps): upgrade to Dart 3.13

[marcossevilla]

Upgrade this package to support Dart 3.13.0.

• Bump the sdk constraint in pubspec.yaml
• Verify tests and lints pass on the new SDK

[unicoderbot]

Great, I will work on a PR and push it soon.

• Preparing environment
  • Cloning repository
  • Setting up dev environment
• Working on changes
• Reviewing changes
• Opening pull request

I've opened a draft pull request: #132

The coding agent reported the work is incomplete: Constraints bumped in both pubspecs, but tests/lints couldn't be verified because only Dart 3.12.2 is installed in this environment.