[Workers] Correct and expand Workers Caching docs

[zaidoon1]

Round of corrections and additions based on review against pingora-origin and edgeworker cache-handler source.

Corrections:

• Responses with no Cache-Control are cached by default via RFC 9111 heuristic freshness; the docs previously said the opposite. Add a table of the 10 default-cacheable status codes and their TTLs.
• s-maxage, must-revalidate, and proxy-revalidate disable both stale-while-revalidate and stale-if-error, not just s-maxage with SWR.
• no-cache caches with zero freshness rather than bypassing. Document the EXPIRED, REVALIDATED, and UPDATING outcomes precisely.
• x-forwarded-scheme rule was reworded incorrectly; restored.

Additions:

• stale-if-error section, including the default (infinite) and the carve-out for s-maxage / must-revalidate / proxy-revalidate.
• 520-526 and 206 are never cached, even with explicit Cache-Control.
• Cache Deception Armor activation conditions for the heuristic- freshness path.
• GET and HEAD share a single cache entry; HEAD on a cold cache is converted to GET internally.
• Custom RPC methods and WebSocket upgrades bypass the cache.
• Cloudflare-Workers-Version-Key request header is part of the cache key.
• Cache-Tag character set (printable ASCII), 1024 chars per tag, 1000 tags per response, case-insensitive purge matching, silent drop of invalid tags.
• Standardized the Cf-Cache-Status value list across files.
• tags and pathPrefixes can be combined in a single purge() call.
• Cf-Cache-Status: STALE debugging section.

Summary

Screenshots (optional)

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• If a larger change - such as adding a new page- an issue has been opened in relation to any incorrect or out of date information that this PR fixes.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.

[cloudflare-docs-bot]

Review

✅ No style-guide issues found in commit 6245639.

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