Better modularization of StorageSlot.sol::getAddressFromSlot()

getAddressFromSlot() is both used to set addresses into precalculated storage slots (returning a reference of the AddressSlot struct), and to get addresses stored into that slot. I guess it would be better to separate the setter from the getter, which I've already done in the code below. There's no need to reassign the storage slot of the struct everytime we need to read the value.

Start in StorageSlot.sol at getAddressFromSlot() and inspect its two current call patterns: setting and reading precalculated slots. Compare the separation proposed in the issue's attached example, then run the relevant existing contract tests to confirm both behaviors remain intact and address reads no longer reassign the storage slot.