Currently, the chain_id is hardcoded in certain places in the `t8n` tool. We need to look into making it more flexible. See [this](https://github.com/ethereum/execution-specs/blob/forks/osaka/src/ethereum_spec_tools/evm_tools/t8n/t8n_types.py#L217-L219) and [this](https://github.com/ethereum/execution-specs/blob/forks/osaka/src/ethereum_spec_tools/evm_tools/loaders/transaction_loader.py#L43-L45) for example.
