[eth] Some contract improvements

[ali-behjati]

This PR:

• Updates contract to use the latest solidity sdk and updates getUpdateFee method to get the data instead of size (+ addressing tests + relayer). Keeps the old one for backward compatibility.
• Removes part of the code to transfer back extra paid fee amount (to be consistent with other chains that do not support it. e.g., aptos)

[jayantk]

I don't think we can make breaking API changes anymore. We don't know for sure that nobody is using us, and we need to be careful.

I think a better solution here would be to mark the old method as deprecated and add a new method that took the full payload.

We could also promise that the old method returns an overestimate of the necessary fee, so everything will continue to work for any users of the old method.

[ali-behjati]

I think this is an unrealistic assumption but I'm not 100% sure. I am sure that no one has communicated to us that they are even trying us out. Also, I can check that no transaction in mainnet has made to update the prices. Keeping it is an extra liability to make sure it's always over estimating.

However, I can get the point that we publicly announced our launch and we should stick to backward compatibility. There's no way to say which one outweighs another one. So as you both like to keep it backward compatible I added the old one too.

[njk-64]

lgtm