docs: enhance JSDoc standards and document package structure (#7182)

CONTRIBUTING.md
- Add guideline to never use 'any' type in JSDoc annotations

AGENTS.md
- Add package structure section explaining src/test directory layout
- Add guideline to never use 'any' type in JSDoc annotations
- Remove redundant Node.js core module prefix bullet point

Author: watson

AGENTS.md

@@ -24,6 +24,14 @@ dd-trace is the Datadog client library for Node.js.
 - `integration-tests/` - E2E integration tests
 - `benchmark/` - Performance benchmarks
 
+**Package Structure:**
+
+Each package follows a consistent structure:
+- `src/` - Source code for the package
+- `test/` - Unit tests for the package
+- Unit test files always follow the `*.spec.js` naming convention
+- Test directories may also contain helper files (e.g., `naming.js`, `helpers.js`, `suite.js`) and integration test subdirectories
+
 ## Testing Instructions
 
 ### Testing Workflow
@@ -113,7 +121,10 @@ assertObjectContains(response, { status: 200, body: { user: { name: 'Alice' } }
 ### Linting & Naming
 - Lint: `yarn lint` / `yarn lint:fix`
 - Files: kebab-case
-- JSDoc: TypeScript-compatible syntax (`@param {string}`, `@returns {Promise<void>}`, `@typedef`)
+
+### JSDoc
+- Use TypeScript-compatible syntax (`@param {string}`, `@returns {Promise<void>}`, `@typedef`)
+- Never use `any` (be specific or use `unknown` if type is truly unknown)
 
 ### Import Ordering
 
@@ -143,7 +154,6 @@ const log = require('../log')
   const { NODE_MAJOR } = require('./version')
   if (NODE_MAJOR >= 20) { /* Use Node.js 20+ API */ }
   ```
-- **Prefix Node.js core modules with `node:`** (e.g., `require('node:assert')`)
 
 ### Performance and Memory
 

CONTRIBUTING.md

@@ -240,10 +240,12 @@ DD_TRACE_DEBUG=true node your-app.js
 DD_TRACE_DEBUG=true yarn test:debugger
 ```
 
-### Documentation
+### JSDoc
 
 Document all APIs with TypeScript-compatible JSDoc to ensure proper types without using TypeScript. This enables type checking and IDE autocompletion while maintaining the JavaScript codebase. Use TypeScript type syntax in JSDoc annotations (e.g., `@param {string}`, `@returns {Promise<void>}`).
 
+Never use the type `any` - be specific.
+
 ## Adding New Configuration Options
 
 To add a new configuration option: