Create comprehensive GitHub Copilot instructions and fix environment.yml YAML syntax

[Copilot]

This PR adds a comprehensive .github/copilot-instructions.md file that provides GitHub Copilot coding agents with detailed instructions on how to work effectively with the QuantEcon/.github repository, and fixes critical YAML syntax errors in environment.yml.

Fixed environment.yml YAML Syntax

Corrected missing colons after name, channels, and dependencies and fixed incorrect pip section structure (was - pip followed by indented items, now properly structured as - pip:). The YAML syntax is now valid and conda env create -f environment.yml works directly.

Comprehensive Copilot Instructions

The instructions document the correct conda environment setup process with timing expectations (15+ minutes), include validated commands for building Jupyter Book lecture repositories (~4 minutes each), and provide complete CI workflow simulation commands with critical timing information. All commands include "NEVER CANCEL" warnings with specific timeout recommendations.

Version-Agnostic Design: The instructions avoid hardcoded version numbers and instead reference version information generically (e.g., "Jupyter Book version information" rather than specific versions). This ensures the instructions remain accurate as the environment.yml file is updated over time.

Key Documentation Areas

• Environment Setup & Build Process: Environment creation takes 15 minutes (30+ minute timeout recommended), single lecture builds take 4 minutes (15+ minute timeout recommended), and full CI workflow takes 25+ minutes (45+ minute timeout recommended)
• Comprehensive Validation & Troubleshooting: Step-by-step validation scenarios for testing changes, expected output examples for successful commands, manual verification procedures, and complete troubleshooting guide for network timeouts and build warnings
• Repository Structure Documentation: Details of GitHub Actions workflows for Linux, macOS, and Windows testing, explanation of the 4 different lecture repositories that are tested, and key files and their purposes

The instructions follow an imperative tone and start with a firm directive to always follow the provided instructions first before searching for additional context. All commands have been validated through actual testing during development.

Fixes #8.

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[mmcky]

@copilot I have noticed you have corrected the environment.yml file. Can you suggest an update to it so you don't have to print it in the copilot-instructions?

[Copilot]

@copilot I have noticed you have corrected the environment.yml file. Can you suggest an update to it so you don't have to print it in the copilot-instructions?

I've updated the environment.yml file to fix the YAML syntax errors (missing colons and incorrect pip section structure) and simplified the copilot-instructions.md to reference the now-working environment.yml directly instead of including an inline corrected version. The environment.yml now has proper YAML syntax and can be used directly with conda env create -f environment.yml. Commit: ee78c24

[mmcky]

@copilot the versions in these instructions will get updated from time to time as environment.yml file is updated.

So please be aware these instructions may become out of date when we update the environment file.

[Copilot]

@copilot the versions in these instructions will get updated from time to time as environment.yml file is updated.

So please be aware these instructions may become out of date when we update the...

You're absolutely right. I've updated the copilot-instructions.md to remove hardcoded version numbers and make them version-agnostic. The instructions now reference "Jupyter Book version information" instead of specific versions, and the expected output examples use placeholder formats (like "1.0.x.postX") instead of exact version numbers. This will keep the instructions accurate as the environment.yml file gets updated over time. Commit: 7bfcfd6