[Contract] Turn `CoreEngine.sol` into a clearly scoped EVM-side protocol boundary

[Solomonsolomonsolomon]

Decide whether CoreEngine.sol is a real cross-chain execution surface or a legacy artifact, then either formalize its responsibilities or redesign it into a coherent EVM integration boundary.

[victorocheje]

@victorocheje has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

I would like to work on this issue

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[manueldezman]

@manueldezman has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hello maintainer, i would like to work on this, will submit a PR within 1 hour, kindly assign to me

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[fairbid01]

@fairbid01 has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hello maintainer, I would like to work on this issue.

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[devcarole]

@devcarole has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hi Maintainer,
I would love to fix this issue

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