EIP-7676: EOF - Prepare for Address Space Extension

A very small change to EOF to allow future extension of the address space.

TL;DR all operations that use an address will not trim the high 12 bytes / 96 bits, and (for now) exceptionally halt if they are not zero. Only BALANCE is not otherwise spoken for within EOF. Future uses of these high bits would necessarily change this behavior. but they are not defined in this EIP.