feat: Contact us unit test

[jeffrey0606]

Description

• add a contact us bloc
• add an infrastructure for contact us repository facade
• create unit tests for the bloc

Type of Change

• [x] ✨ New feature (non-breaking change which adds functionality)
• [ ] 🛠️ Bug fix (non-breaking change which fixes an issue)
• [ ] ❌ Breaking change (fix or feature that would cause existing functionality to change)
• [ ] 🧹 Code refactor
• [ ] ✅ Build configuration change
• [ ] 📝 Documentation
• [ ] 🗑️ Chore

Pre-launch Checklist

• [ ] I read the Contributor Guide and followed the process outlined there for submitting PRs.
• [ ] I read and ran all relevant commands as specififed in the Running Tests section of the Contributor Guide.
• [ ] The title of the PR follows the Conventional Commits guideline
• [ ] My local branch follows the naming standards in the Deepsource Branch Naming Convention or Biodiversity Branch Naming Convention
• [ ] I listed at least one issue that this PR fixes in the description above.
• [ ] I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy,
• [ ] I updated/added relevant documentation (doc comments with ///).
• [ ] I added new tests to check the change I am making, or this PR is [test-exempt].
• [ ] All existing and new tests are passing.