Zero-memory caches keep resolved cache life in dev

Misc Changes

• docs(cache-components): clarify allow-runtime, sync-IO and instant=false, CLS fallback: #94997
• Keep the resolved cache life for cacheMaxMemorySize: 0 caches in dev: #95100
• Avoid mutating req.headers when stripping internal headers: #95116

Credits

Huge thanks to @aurorascharff and @unstubbable for helping!