fix(interopgen): honor InteropOffset when setting UseInterop at genesis

[maurelian]

Summary

GenesisL2 unconditionally set UseInterop = true and enabled the Interop dev feature bit for every multi-chain setup, ignoring the configured InteropOffset. When InteropOffset > 0, this created an impossible configuration: the Solidity fork number is pre-Interop, but genesis was told to install Interop contracts and feature flags anyway.

Now UseInterop and DevFeatureBitmap are derived from whether Interop actually activates at genesis (InteropOffset == 0), not from whether the world has multiple chains.

Test plan

• Existing TestInteropDevRecipe (offset=0, 2 chains) passes — behavior unchanged
• TestInteropUpgrade (offset=3, 2 chains) can now build genesis without conflict
• TestInteropGenesisActivation (offset=0) passes — behavior unchanged

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.5%. Comparing base (45287f7) to head (7c15e95).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop   #20029      +/-   ##
===========================================
+ Coverage     11.7%    74.5%   +62.8%     
===========================================
  Files          676      193     -483     
  Lines        71016    10734   -60282     
===========================================
- Hits          8322     8002     -320     
+ Misses       62550     2588   -59962     
  Partials       144      144              

Flag	Coverage Δ
cannon-go-tests-64	66.3% <ø> (ø)
contracts-bedrock-tests	79.4% <ø> (ø)
unit	?

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