chore: Prepare the repository to use GitHub Copilot

.github/copilot-instructions.md

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+# Drift Offline First Project Guidelines
+
+- Before starting any task, CONSIDER ALL GUIDELINES from this document.
+- If a guideline that is directly related to the task contains a reference,
+  fetch the reference to improve the understanding of the task.
+
+## Project Context
+
+- This package is a non-invasive plugin implementation of offline-first
+  features for Drift that uses CRDT (conflict-free replicated data types) for
+  conflict resolution.
+- The package is in early stages and more documentation will be added as it
+  evolves. Currently, rely on the code and comments to understand how it works.
+  Although extensive docs are not present, the code is well-documented and the
+  tests are comprehensive.
+
+## General Guidelines
+
+- Always conform to the coding style of the existing code.
+- Remove unnecessary comments from production code.
+- Ensure linting passes before considering the task finished.
+
+## Pubspec Dependency Management
+
+- Do not add any new dependencies, unless explicitly asked.
+- If a new dependency is needed, ask for permission first.
+
+## Testing Guidelines
+
+- Use the existing test framework and follow the existing patterns or similar
+  tests/examples.
+- The [utils](../test/utils) folder contains utility functions and classes that
+  are used to simplify test setup and teardown.
+- Always follow the AAA pattern (Arrange-Act-Assert) on tests.
+- Avoid comments like '// Arrange', '// Act', '// Assert'.
+- Avoid mocks on tests. Try to use as much real code as possible.
+- Check other tests to see how test data is being created.
+- Tests should validate expected behavior and results, never implementation
+  details.
+- Focus tests specially in dynamic behaviors and edge cases.
+- Separate into groups to make them more readable.
+- Avoid overlapping tests. Tests should validate different aspects of the code.
+- If tests are broken, only finish when they are all passing or you need
+  guidance.
+- NEVER fix a test by reducing its scope.
+- NEVER remove tests without a good reason.
+
+### Test Description Pattern
+
+Use the "Given, when, then" pattern for test descriptions to maintain
+consistency:
+
+```dart
+test(
+  'Given [initial state] when [action performed] then [expected outcome].',
+  () {
+    // Test implementation
+  }
+);
+```
+
+**CRITICAL**: When using `group()` with `test()`, ensure each statement
+("Given", "when", "then") appears **only once** in the combined description:
+
+```dart
+// CORRECT: "Given" in group, "when/then" in test
+group(
+  'Given a session with slow method call when logging is enabled',
+  () {
+    test(
+      'when session is logged then time field should be set to start time.',
+      () {
+        // Test implementation
+      }
+    );
+  }
+);
+
+// INCORRECT: "Given" repeated in both group and test
+group(
+  'Given a session with slow method call',
+  () {
+    test(
+      'Given a slow method when session is logged then time field is correct.',  // ❌ Duplicate "Given"
+      () {
+        // Test implementation
+      }
+    );
+  }
+);
+```
+
+### Test Organization
+
+- Place passing/success test cases at the top of test files
+- Group related test cases using `group()` where appropriate
+- Follow success test cases with error test cases for the same functionality
+
+## Pull Request Guidelines
+
+Before submitting a PR, ensure:
+
+1. **Title follows conventional commits format**: See section below.
+2. **Code is formatted**: `dart format .`
+3. **Linting passes**: `dart analyze .`
+4. **Tests pass**: Always run all tests with `dart test`, since they are fast.
+5. **No excessive documentation**: Only add documentation if explicitly asked.
+
+### PR Title Format
+
+```
+<type>: <description>
+```
+
+**Valid types** (enforced by GitHub Actions):
+
+- **`feat`**: New features
+- **`fix`**: Bug fixes
+- **`docs`**: Documentation changes
+- **`style`**: Code style changes (formatting, missing semi-colons, etc)
+- **`refactor`**: Code refactoring without changing functionality
+- **`perf`**: Performance improvements
+- **`test`**: Adding or updating tests
+- **`build`**: Changes to build system or dependencies
+- **`ci`**: Changes to CI configuration files and scripts
+- **`chore`**: Maintenance tasks, tooling changes
+- **`revert`**: Reverting previous commits
+
+**Requirements**:
+
+- Description must start with an uppercase letter
+- Be descriptive and concise
+- Use imperative mood ("Add feature" not "Added feature")
+
+**Examples**:
+
+```
+feat: Add authentication module for OAuth2 integration
+fix: Resolve database connection timeout issue
+docs: Update installation guide with Docker requirements
+refactor: Simplify error handling in client package
+test: Add integration tests for chat module
+chore: Update dependencies to latest versions
+```

.github/workflows/copilot-setup-steps.yaml

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+name: "Copilot Setup Steps"
+
+on:
+  workflow_dispatch:
+  push:
+    paths:
+      - .github/workflows/copilot-setup-steps.yml
+  pull_request:
+    paths:
+      - .github/workflows/copilot-setup-steps.yml
+
+jobs:
+  copilot-setup-steps:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Set up Dart
+        uses: dart-lang/setup-dart@v1
+        with:
+          sdk: stable
+
+      - name: Install all dependencies
+        run: dart pub get