PR Summary

Medium Risk
Default-on parallel EVM execution changes production behavior for nodes without explicit opt-out; blocktest isolation limits test impact.

Overview
Turns on the Giga executor and OCC by default for nodes: DefaultConfig now sets both enabled and occ_enabled to true, and the generated TOML template comments reflect those defaults. Config keys that are missing (older files) therefore resolve to Giga + OCC unless explicitly set to false.

The blocktest CLI overrides Viper to disable Giga and OCC before building the app, so Ethereum Foundation block tests keep using the standard EvmKeeper / reference EVM path instead of the parallel Giga engine (which would not match how those tests assert state).

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Codecov Report

❌ Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 58.18%. Comparing base (3c0c729) to head (238dbf8).

@@            Coverage Diff             @@
##             main    #3521      +/-   ##
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- Coverage   59.18%   58.18%   -1.01%     
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  Files        2210     2139      -71     
  Lines      183250   173506    -9744     
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- Hits       108455   100949    -7506     
+ Misses      65003    63565    -1438     
+ Partials     9792     8992     -800