doc: improve dual package hazard section with node/default pattern

[ajeeth-asperand]

Fixes: #52174

What

Expands the "Dual CommonJS/ES module packages" section in doc/api/packages.md
to describe the dual package hazard and recommend using "node" / "default"
conditions for dual packages, with a small package.json example.

Why

The existing section only linked to the package examples repository without
describing the recommended pattern. Using "node" / "default" conditions
helps avoid the dual package hazard in Node.js while still allowing other
environments (such as bundlers) to consume an ES module build.

How

• Described the dual package hazard in more detail.
• Documented the "node" / "default" export conditions pattern.
• Added an example package.json snippet.

Testing

• python tools/test.py doctool

[nodejs-github-bot]

Review requested:

• @nodejs/loaders

[tats-u]

Where is module-sync?

[JakobJingleheimer]

Thank you, but we already have that covered; it was formerly in the API docs but was moved to a Learn article: https://nodejs.org/en/learn/modules/publishing-a-package

[tats-u]

Also we should note that more and more packages in the wild have become ESM-only recently and all Node versions without support for module-sync (older than 20) are EOL today.