Add TypeScript type definitions for JavaScript modules

[Copilot]

Description

Adds TypeScript type definitions (.d.ts) for all modules in src/, enabling IDE autocomplete and type checking for TypeScript consumers.

Changes:

• Added TypeScript 5.9.3 as dev dependency
• Created tsconfig.json configured to generate declaration files from JavaScript sources
• Added JSDoc annotations to module exports for accurate type inference
• Updated package.json:
  • "types": "./src/index.d.ts" field points to type definitions
  • "build": "tsc" script generates .d.ts files
• Generated type definitions preserve exports:
  • Logger returns winston.Logger with proper options interface
  • Redis returns ioredis.Redis | undefined with exported getConnectionInfo function
  • Server returns object with app, server, listen(), close() methods
  • NewRelic returns initialization result or undefined

TypeScript consumers now get full IntelliSense:

import { logger, redis, server } from '@automattic/vip-go';

// Autocomplete and type checking work
const log = logger('my-app:module', {
  transport: customTransport,  // Type: winston-transport
  silent: false                 // Type: boolean
});

const redisClient = redis({ logger: log });  // Type: Redis | undefined

Steps to Test

1. Check out PR
2. Run npm install
3. Run npm run build to generate type definitions
4. Verify .d.ts files exist in src/ subdirectories
5. Run npm test to verify all tests pass
6. Create a TypeScript file importing the package and verify IDE autocomplete works

Original prompt

Please generate TypeScript typings for sources in src/ and update package.json. Then create a PR with your changes.

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