eth contract: replace error with other var names

[ppca]

error (Special Solidity Feature)

Introduced in Solidity 0.8.4.
Allows defining custom errors that can be used with revert, making reverts more gas-efficient compared to require with string messages.
Example:

error Unauthorized(address user);

function restrictedFunction() public {
    if (msg.sender != owner) {
        revert Unauthorized(msg.sender);
    }
}

Using error is cheaper than reverting with a string message because it avoids storing large strings in transaction logs.

We should not use error as variable name