Fix MaruCluster config after merge regression

[fluentcrafter]

Note

Make validator EL optional and wire engine/L2 ETH endpoints from ElNode via ForkTransition and updated defaults.

• test-utils:
  • Config defaults (MaruConfigHelper.kt):
    • Add forkTransition = ForkTransition().
    • Remove default validatorElNode; now null by default.
  • Validator/EL setup:
    • setValidatorConfig is a no-op when elNode is null.
    • When present, updates validatorElNode.engineApiEndpoint and forkTransition.l2EthApiEndpoint from elNode URLs; creates ValidatorElNode if missing.
• App factory (TestMaruAppFactory.kt):
  • Call setValidatorConfig earlier in createMaru before other config mutations.

^{Written by Cursor Bugbot for commit 42dfe7d. This will update automatically on new commits. Configure here.}

[codecov-commenter]

Codecov Report

❌ Patch coverage is 64.70588% with 6 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (main@be0fb67). Learn more about missing BASE report.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
.../main/kotlin/maru/test/cluster/MaruConfigHelper.kt	62.50%	3 Missing and 3 partials ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #459   +/-   ##
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  Coverage        ?   83.00%           
  Complexity      ?     1104           
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  Files           ?      226           
  Lines           ?     7992           
  Branches        ?      624           
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  Hits            ?     6634           
  Misses          ?     1013           
  Partials        ?      345           

Flag	Coverage Δ
kotlin	83.00% <64.70%> (?)

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