[aztec-smart-contracts] Investigate how storage.at() works under the hood

[smanilov]

See this conversation: https://github.com/blocksense-network/blocksense/pull/481/files#r1780787377

[zah]

Most specifically, my question was whether at is a Noir library function (that will be compiled to many constraints) or some sort of a built-in magic in the Aztec smart contract execution environment? We should be able to answer this question by inspecting/debugging the compilation process for the smart contract.