Cloudflare instrument Flagship (feature flags)

### Problem Statement

Flagship is now in public beta since May 26, 2026: https://developers.cloudflare.com/changelog/post/2026-05-26-public-beta/

Would be helpful to have this value in the trace to analyze further spans: https://developers.cloudflare.com/flagship/get-started/

### Solution Brainstorm

Use `instrumentEnv` to instrument it.

### Additional Context

_No response_

### Priority

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