Here I am proposing two small changes to the exported API for EIP-7702:
(1) `Authorization` has a very generic name, but it is in fact only used
for one niche use case: authorizing code in a `SetCodeTx`. So I propose
calling it `SetCodeAuthorization` instead. The signing function is
renamed to `SignSetCode` instead of `SignAuth`.
(2) The signing function for authorizations should take key as the first
parameter, and the authorization second. The key will almost always be
in a variable, while the authorization can be given as a literal.
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