Add GitHub Copilot instructions for o1js development workflow

[Copilot]

This PR adds comprehensive GitHub Copilot instructions to help coding agents work effectively in the o1js codebase. The instructions provide detailed guidance on building, testing, and developing with o1js while working around its complex build requirements.

Key Features

Build Process Guidance:

• Clear setup requirements (Node.js 18.14+, npm, GitHub CLI, git submodules)
• Step-by-step initialization with proper timing expectations
• Explicit timeout values and "NEVER CANCEL" warnings for long operations
• Alternative approaches when full build fails

Validated Commands with Timing:

• npm install (18 seconds)
• git submodule update --init --recursive with LFS skip (5 minutes)
• npm run lint (2 seconds, shows expected warnings)
• Independent src/mina-signer build and test workflow (37 seconds total)

Critical Build Limitations:
The instructions clearly document that o1js requires pre-compiled OCaml/Rust bindings from CI builds, which external contributors cannot generate without GitHub authentication. This is a core architectural constraint that affects the development workflow.

Working Validation Scenarios:

• Syntax validation through linting without full build
• Independent testing of the mina-signer cryptographic library
• Format checking for markdown and code style
• Manual validation approaches for functionality testing

Comprehensive Troubleshooting:

• Common error messages and their solutions
• Workarounds for build authentication issues
• Guidance on when operations are expected to take 15-45+ minutes
• Project structure reference for navigation

The instructions follow an imperative tone ("Run this command", "Set timeout to X") and provide exhaustive detail to ensure agents can copy-paste commands that work reliably every time.

Fixes #2386.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• esm.ubuntu.com
  • Triggering command: /usr/lib/apt/methods/https (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

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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.