Fix/cross chain hash message 293

[rabsqueen]

Summary

Fixes a critical compilation error in cross_chain_verifier caused by two private hash_message implementations with effectively identical logic.

Both implementations generated the cross-chain message hash using the CROSS_CHAIN_MESSAGE_V1 domain prefix and the same message fields, resulting in a duplicate function definition within the contract.

What Changed

🐛 Removed Duplicate Implementation

• Removed the redundant hash_message function.
• Retained the cleaner implementation using Bytes::from_slice.
• Preserved the existing CROSS_CHAIN_MESSAGE_V1 domain separator.
• Preserved the existing message fields and hashing order.

🔐 Hashing Behaviour Preserved

The retained implementation continues to construct the message hash using the established cross-chain domain:

CROSS_CHAIN_MESSAGE_V1
        +
Cross-chain message fields
        ↓
Deterministic hash

No changes were made to the intended hashing scheme or message format.

Before

impl CrossChainVerifier {
    fn hash_message(...) {
        // Implementation A
    }

    ...

    fn hash_message(...) {
        // Implementation B ❌
    }
}

The duplicate private function caused the contract to fail compilation.

After

impl CrossChainVerifier {
    fn hash_message(...) {
        // Consistent Bytes::from_slice implementation
        // CROSS_CHAIN_MESSAGE_V1
        // Same message fields and hashing order
    }
}

A single authoritative implementation now handles cross-chain message hashing.

Validation

Verified that:

• Only one hash_message implementation remains.
• The retained implementation consistently uses Bytes::from_slice.
• CROSS_CHAIN_MESSAGE_V1 remains unchanged.
• Message fields and hashing order are preserved.
• Existing signature verification compatibility is maintained.
• The contract compiles successfully.

Acceptance Criteria

• Remove one of the duplicate hash_message implementations.
• Retain the cleaner Bytes::from_slice implementation.
• Preserve CROSS_CHAIN_MESSAGE_V1.
• Preserve the existing message hashing logic.
• Restore successful contract compilation.

Result

cross_chain_verifier now contains a single, consistent hash_message implementation, eliminating the critical build failure while preserving the established cross-chain message hashing scheme.

Closes #292
Closes #293
Closes #295
Closes #294

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