fix(interopgen): use InteropOffset when setting Interop genesis flags

[0xiamflux]

Summary

GenesisL2 was enabling UseInterop and OptimismPortalInteropFlag based entirely on whether the world had more than one chain. This caused L2Genesis.s.sol to reject the configuration with L2Genesis_InvalidInteropConfig whenever InteropOffset > 0, because the fork number at genesis would be pre-Interop while both flags were set.

Changes

• Gate both flags on multichainDepSet && interopOffset == 0. Interop will only be enabled at genesis if it's actually scheduled to activate.

Closes #20079

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 66.3%. Comparing base (30a1dbf) to head (8b6e177).
⚠️ Report is 1 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop   #20148      +/-   ##
===========================================
+ Coverage     11.5%    66.3%   +54.7%     
===========================================
  Files          668       55     -613     
  Lines        72125     4035   -68090     
===========================================
- Hits          8332     2677    -5655     
+ Misses       63649     1214   -62435     
  Partials       144      144              

Flag	Coverage Δ
cannon-go-tests-64	66.3% <ø> (ø)
contracts-bedrock-tests	?
unit	?

Flags with carried forward coverage won't be shown. Click here to find out more.
see 613 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.