Eth contract fix memory + new sdk + refactor

[ali-behjati]

• Change some memory modifiers to improve gas efficiency
• Implement getValidTimePeriod() and remove old staleness logic
• Update the tests

[ali-behjati]

I have used a placeholder bytes and i'm replacing it within the deployment process I replace the placeholder with the hash in the contract binary.. So it's not part of the contract and return hex"123123..." doesn't look quite clean.

@tompntn raised it and suggested to use a storage variable instead, and a method like setGitCommitHash() to set as the migration call in the upgradeProxy. However, I think it's too much to have it as a migration call. We are likely to use migrate functions and then in each of them we should make sure this hash is set correctly. Also, the nature of this hash is not a variable to be set. In the placeholder version it's within the implementation code and won't change (tied to implementation). In the storage variable it's in the proxy storage and will change every time.

I decided to move on with the existing placeholder approach (although it doesn't look nice), I am not particularly happy with it. We definitely can revisit it. We can change to migration call whenever needed in the future too and we just need to change the underlying value of deployCommitHash.

Posted a summary here for future reference when we get back to it.