Add copilot instructions for reviews

Author: alcaeus

.github/copilot-instructions.md

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+# GitHub Copilot Instructions
+
+## Code Review Guidelines
+
+### Review Focus
+- **Do not repeat or paraphrase the PR description**
+- Only highlight changes or notable information that was omitted from the description
+- Focus on code quality, potential issues, and improvements not mentioned in the PR
+
+### PHP Version and Type Requirements
+- Code must support **PHP 8.1 and newer**
+- Use **full type declarations** wherever possible
+- Leverage PHP 8.1+ features when appropriate (enums, readonly properties, intersection types, etc.)
+- Use **PHPDoc blocks** to supplement native types where PHP limitations exist:
+  - Generics: `@template T`, `@param Collection<T>`, `@return T`
+  - Union types for complex scenarios
+  - Array shapes: `@param array{name: string, age: int}`
+  - More specific types than native PHP allows
+
+### Code Quality Standards
+- Ensure all public methods have complete type hints
+- Private/protected methods should also be fully typed
+- Use strict scalar type declarations (`declare(strict_types=1)`)
+- Prefer constructor property promotion when applicable
+- Use named arguments for better readability in complex method calls
+
+### MongoDB Library Specific
+- Check for proper error handling patterns
+- Ensure BSON type handling is correct
+- Verify connection pool and client usage follows best practices
+- Look for potential performance implications in database operations
+- Ensure proper use of type maps and codecs
+
+### What to Flag in Reviews
+- Missing type declarations that could be added
+- Opportunities to use newer PHP features
+- Code that might not work with the minimum PHP 8.1 requirement
+- Missing PHPDoc for complex types or generics
+- Inconsistent coding standards
+- Potential performance or security issues not mentioned in PR description
+- Breaking changes that weren't highlighted
+- Documentation that needs updating due to code changes
+
+### What NOT to Comment On
+- Changes that are clearly explained in the PR description
+- Style preferences that are already covered by existing linting tools
+- Minor formatting issues that automated tools should catch