Create comprehensive .github/copilot-instructions.md with validated build procedures and OpenSSL 3.2.0 requirements

[Copilot]

This PR adds a comprehensive .github/copilot-instructions.md file that provides detailed instructions for GitHub Copilot coding agents on how to work effectively with the Cosmian CLI codebase.

Key Features

Validated Build Procedures: All commands have been tested and timed in a fresh repository clone:

• Git submodule initialization (~30 seconds)
• Development builds with cargo check (~1 minute)
• Release builds (~8 minutes)
• Full test suite execution (~11 minutes)
• Code formatting and linting (~17 seconds)

OpenSSL 3.2.0 Requirements: Specifies the exact OpenSSL version requirement throughout the documentation:

• Prerequisites section emphasizes OpenSSL 3.2.0 installation
• Build troubleshooting section clarifies version requirements
• Environment setup instructions reference specific version compatibility
• Cross-platform support documentation updated for version consistency

Critical Timeout Guidance: Includes explicit "NEVER CANCEL" warnings with specific timeout recommendations for long-running operations to prevent premature cancellation of builds and tests.

End-to-End Validation Scenarios: Provides complete workflows for testing:

• KMS operations (key creation, encryption, decryption)
• Findex server integration
• Docker service management
• CLI functionality validation

Environment Setup: Documents the exact OpenSSL 3.2.0 configuration required:

export OPENSSL_LIB_DIR=/usr/lib/x86_64-linux-gnu
export OPENSSL_INCLUDE_DIR=/usr/include/openssl
export PKG_CONFIG_PATH=/usr/lib/x86_64-linux-gnu/pkgconfig

Common Issues and Workarounds: Addresses known limitations:

• Network connectivity issues with external OpenSSL downloads
• Integration test script port configuration problems
• Expected test failures in restricted environments
• Build performance optimization tips

Developer Workflow: Provides a complete reference for:

• Repository initialization and submodule management
• Quick development iteration cycles with OpenSSL 3.2.0
• Docker service setup and troubleshooting
• Code quality checks and CI preparation

The instructions follow the specified format with imperative tone commands, exhaustive validation of every procedure, and specific timing expectations to ensure reliable development workflows with proper OpenSSL version compatibility.

Fixes #93.

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💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.