Add Dev Container for MSML Development

[rororowyourboat]

Context

Setting up the MSML development environment requires manual dependency installation and implicit knowledge of the toolchain. This increases onboarding time and leads to environment drift across contributors.

A standardized dev container would make MSML easier to develop, test, and contribute to.

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Goals

• Provide a reproducible development environment
• Reduce setup friction for new contributors
• Align local development with CI expectations

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Scope

• Add a .devcontainer/ configuration
• Preinstall required system dependencies and Python tooling
• Include common developer tools (linting, formatting, testing)
• Ensure compatibility with VS Code Dev Containers and GitHub Codespaces

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Deliverables

• .devcontainer/devcontainer.json
• Dockerfile (if needed)
• Brief README section explaining how to use the dev container

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Non-Goals

• Production Docker images
• Heavy optimization or multi-stage builds