ContractId
A contract's ID is a unique, deterministic identifier analogous to a contract's address in the EVM. Contracts cannot own UTXOs but they can own assets.
The ContractId type is a struct containing a value of a b256 type.
pub struct ContractId {
    bits: b256,
}
Casting between an ContractId and b256 can be done in the following way:
    let variable1 = 0x000000000000000000000000000000000000000000000000000000000000002A;
    let my_contract_id = ContractId::from(variable1);
    let variable2: b256 = my_contract_id.into();
    // variable1 == variable2