CSE: propagate immutable values to `program`/`code` cells

If a function we’re CSE-ing calls a function from a contract that has immutables, then the code we have to put into the account cell of that contract has to be the post-constructor-execution code, not the code with zeros where the immutables are.

One idea is to add a property similar to contract.has_immutables for a contract based on its AST, and then get the cell from the corresponding contract.init proof for it to be inserted into the <code> cell of the new account.

Start by tracing the CSE handling of account, program, and code cells, then inspect the contract.has_immutables logic and the corresponding contract.init proof. Confirm how the init proof exposes its output cell. Done means immutable values from post-constructor code are propagated into the new account's code cell instead of remaining zeroed.