[jdjioe5-cpu]

What

Ensure commands that send or simulate transactions always output diagnostic events when there is a failure, and ensure diagnostic events are logged when using --very-verbose.

Specifically:

• In simulate_and_assemble_transaction (cmd/soroban-cli/src/assembled.rs):
  • When sim_res.error is present (simulation failed), diagnostic failure events are rendered via crate::log::event::failure(&events, &print) in addition to being logged via crate::log::event::all(&events).
  • When simulation succeeds, crate::log::event::all(&events) logs the diagnostic events at debug level (visible under --verbose / --very-verbose).
• In send_transaction_polling_with_events (cmd/soroban-cli/src/tx.rs):
  • When transaction submission succeeds, crate::log::event::all(&res.events.diagnostic_events) is called so that diagnostic events are logged at debug level under --verbose / --very-verbose.
• In cmd/soroban-cli/src/log/event.rs:
  • Use unwrap_or_default() in all(&events) for serialization robustness.
  • Added unit test test_failure_outputs_error_and_log_events verifying failure and diagnostic event handling.

Why

Resolves #2224.
Previously:

1. When a transaction failed during preflight simulation (e.g. host error, contract panic, budget exceeded), diagnostic events decoded by RPC were available on sim_res.events() but only logged at debug level and never rendered to stderr. Users only saw Error::TransactionSimulationFailed without the underlying host/contract error events or diagnostic logs.
2. In --very-verbose mode, successful simulations and successful transaction submissions did not call crate::log::event::all, meaning diagnostic events were completely missing from the debug/trace stream.

Known limitations

None. Backward compatibility is fully preserved.