Improve runtime API difference documentation

[NuroDev]

Summary

As part of cloudflare/workers-sdk#10108 we need to better document the clear boundary between web standard implementations and workerd's. As such, I have updated the runtime API's documentation to include and/or improve a "Differences" section.

Documentation checklist

• Is there a changelog entry (guidelines)? If you don't add one for something awesome and new (however small) — how will our customers find out? Changelogs are automatically posted to RSS feeds, the Discord, and X.
• The change adheres to the documentation style guide.
• If a larger change - such as adding a new page- an issue has been opened in relation to any incorrect or out of date information that this PR fixes.
• Files which have changed name or location have been allocated redirects.

[github-actions]

Preview URL: https://89c89625.preview.developers.cloudflare.com
Preview Branch URL: https://nurodev-fix-runtime-api-differences.preview.developers.cloudflare.com

Files with changes (up to 15)

Original Link	Updated Link
https://developers.cloudflare.com/workers/runtime-apis/response/	https://nurodev-fix-runtime-api-differences.preview.developers.cloudflare.com/workers/runtime-apis/response/
https://developers.cloudflare.com/workers/runtime-apis/request/	https://nurodev-fix-runtime-api-differences.preview.developers.cloudflare.com/workers/runtime-apis/request/
https://developers.cloudflare.com/workers/runtime-apis/headers/	https://nurodev-fix-runtime-api-differences.preview.developers.cloudflare.com/workers/runtime-apis/headers/

[github-actions]

This pull request requires reviews from CODEOWNERS as it changes files that match the following patterns:

Pattern	Owners
/src/content/docs/workers/	@cloudflare/workers-docs, @GregBrimble, @irvinebroque, @mikenomitch, @korinne, @WalshyDev, @cloudflare/deploy-config, @cloudflare/pcx-technical-writing, @cloudflare/wrangler, @mattietk