[build-tools] pass metrics CORS origin to serve-sim

[gwdp]

Why

so the expo.dev dashboard can read serve-sim's live /metrics stream cross-origin.

How

reads EAS_SIMULATOR_METRICS_CORS_ORIGIN from the worker env and passes it to serve-sim as --metrics-cors-origin when launching the tunnel. optional (unset = no cross-origin reads), and a comma-separated value becomes one flag per origin (prod + staging).

Test Plan

CI passes. unit tests cover the env getter and the arg builder.

[gwdp]

• [build-tools] upload serve-sim metrics artifact on session teardown #3995
• [build-tools] pass metrics CORS origin to serve-sim #3990 👈 (View in Graphite)
• main

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[github-actions]

✅ Thank you for adding the changelog entry!

[codecov]

Codecov Report

❌ Patch coverage is 91.66667% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 59.80%. Comparing base (cc42fdc) to head (1230799).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
...ld-tools/src/steps/utils/remoteDeviceRunSession.ts	91.67%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3990      +/-   ##
==========================================
+ Coverage   59.60%   59.80%   +0.21%     
==========================================
  Files         938      936       -2     
  Lines       41226    41069     -157     
  Branches     8678     8639      -39     
==========================================
- Hits        24568    24559       -9     
+ Misses      16564    16416     -148     
  Partials       94       94              

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