fix: state: short-circuit genesis state computation

[arajasek]

Related Issues

@magik6k observed that the recently added TestEthGetGenesis is flaky. The cause is that our state computation of the first epoch needs short-circuiting to handle certain special-casing (eg. a WinCount of 0).

Proposed Changes

This special-casing already exists, but lived one level too high for tooling like StateCompute. Moving it down one level fixes the issue.

Additional Info

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