Add comprehensive GitHub Copilot instructions for lambda-api development

[Copilot]

This PR adds a comprehensive .github/copilot-instructions.md file that provides GitHub Copilot coding agents with detailed instructions for working effectively in the lambda-api codebase.

What's Included

The instructions cover all essential aspects of lambda-api development:

Build and Test Workflow

• Dependencies: npm ci (35 seconds)
• Testing: Complete test suite with timing guidance
  • npm test - Full test suite (12 seconds, 478 tests)
  • npm run test:unit - Unit tests only (6 seconds)
  • npm run test:types - TypeScript validation (4 seconds)
• Code Quality: ESLint and Prettier commands with <1 second execution
• CI Pipeline: npm run test-ci replicating GitHub Actions workflow

Validation Guidelines

The instructions emphasize manual validation with specific test scenarios:

• Basic route creation and JSON responses
• Path parameters (e.g., /users/:id)
• HTTP methods (GET, POST, PUT, DELETE)
• Middleware functionality
• Error handling
• Route debugging with api.routes(true)

Project Context

• Zero dependencies design principle
• No build step required (pure JavaScript)
• 97.63% test coverage across 27 test suites
• Express.js-like API optimized for AWS Lambda
• Serverless architecture patterns

Practical Examples

Working code examples demonstrate:

const api = require('./index.js')();
api.get('/test', (req, res) => res.json({ status: 'ok' }));
const mockEvent = { httpMethod: 'GET', path: '/test', body: null, headers: {}, multiValueHeaders: {} };
api.run(mockEvent, {}).then(result => console.log(result));

Validation Process

All commands and examples were thoroughly tested:

• Measured actual execution times for timeout recommendations
• Verified all code examples work correctly
• Tested complete end-to-end scenarios
• Validated formatting and linting requirements
• Ensured instructions follow "never cancel" guidelines with appropriate timeouts

The instructions enable coding agents to work efficiently without extensive exploration, reducing development time and preventing common mistakes.

Fixes #293.

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:

• coveralls.io
  • Triggering command: node ./node_modules/coveralls/bin/coveralls.js (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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✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.