Add GitHub Copilot instructions for repository

[Copilot]

Configures repository-specific instructions for GitHub Copilot to guide AI-assisted development.

Changes

Created .github/copilot-instructions.md covering:

• Wrapper design patterns: Properties over getters/setters, Pythonic iteration (__iter__, __len__, __getitem__), method chaining, DataFrame integration, dict-like metadata access
• Code conventions: Black (100 char), Python 3.8+, type hints, Py_ prefix for wrapper classes
• Architecture: Wrapper pattern delegating to pyOpenMS, factory methods (from_file, from_dataframe), smart filtering via methods and properties
• Testing: pytest structure, coverage expectations, fixture patterns
• Development: Installation, dependencies, formatting commands
• Common tasks: Adding new wrappers, helper functions, documentation updates
• Performance considerations: Memory management for large datasets, streaming alternatives, minimal wrapper overhead

This follows GitHub's best practices for Copilot coding agent configuration and provides context on the repository's Pythonic abstraction layer over pyOpenMS C++ bindings.

Original prompt

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This section details on the original issue you should resolve

<issue_title>✨ Set up Copilot instructions</issue_title>
<issue_description>Configure instructions for this repository as documented in Best practices for Copilot coding agent in your repository.

</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes ✨ Set up Copilot instructions #22

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