[eth] contract improvement

[ali-behjati]

This PR improves the eth contract by some small changes.

• Renames Pyth.initializeto Pyth._initialize and makes it internal. This method was public and always was confusing although technically it was safe (PythUpgradable overridden it).
• Makes contract upgrade more resillient + add fails test: There is a pythUpgradableMagic method that returns some random number and the upgrades makes sure that this function can be called and it can return the correct value. There is a test to capture it.
  • Unfortunately I couldn't add an increasing version check as string comparison does not exist in solidity (for equality you should hash the string!)
• Removes deploy commit hash. It is very error-prone as not used anywhere. I could add it to the upgrades, but that requires a lot of change and additional overhead to again inject it in the migration step (which we should make sure we are in the right branch). We can add it later if needed.
• Improves the price not found log. This error could happen for an existing price that hasn't received any update on target chain yet. Modified the log to be more verbose.

[jayantk]

lgtm modulo the comment. I think it would be good to have another review from someone with better solidity knowledge than me as well.

[njk-64]

lgtm