const/immutable contract fields

```rust
contract Foo {
mut balance: Map,
creator: Address, // const, written to bytecode

...
```

The issue provides only a contract syntax example and does not name implementation files, tests, or entry points. Start by locating the contract field representation and bytecode generation path, then determine how const or immutable fields should be represented and verify that the resulting contract stores the creator value in bytecode.

Written by the indexing model from the issue text.