Review codebase for PipelineExecutionData exit status usage

[cablehead]

Nushell main now returns PipelineExecutionData from eval_block_with_early_return, which includes:

• .body: the PipelineData (what we currently extract and use)
• .exit: Vec<Option<(Arc<Mutex<ExitStatusFuture>>, Span)>> (currently ignored)

We should review the codebase to determine if/where we should be checking or propagating these exit statuses, particularly in:

• src/nu/engine.rs: eval(), parse_closure(), run_closure_in_job()
• src/nu/config.rs: config loading

Related to upgrade to nushell main branch.