fix(api-server): surface RPC events on simulate response (#1162)

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Summary

SimulateTransactionResult.events was being parsed by the Soroban simulateTransaction deserializer but then dropped on the floor by the simulate handler — confirmed by the #[allow(dead_code)] attribute and a repo-wide grep showing no other reference to the field. The RPCs events array carries diagnostic/contract events (emitted events, failure reasons) that are useful context for callers trying to understand a simulation result, especially one that reports success: false.

Fix

• FeeBreakdown gains an events: Vec<serde_json::Value> field with a doc comment explaining the contract: present but possibly empty on the heuristic fallback path.
• simulate() propagates result.events into the FeeBreakdown on the live-RPC success path; the heuristic fallback path initializes events to an empty vec.
• SimulationDetail in types.rs gains a matching events: Vec<serde_json::Value> field with #[serde(default)] so existing clients deserializing older responses without the field still parse cleanly.
• handlers::simulate populates SimulationDetail.events from the breakdown.

Tests

Both tests stand up an in-process axum mock via tokio::net::TcpListener::bind("127.0.0.1:0") so they do not depend on any fixed port or a live RPC:

• test_simulate_surfaces_rpc_events_in_simulation_detail — mock returns two events (a contract Transfer and a diagnostic message); asserts the API surfaces both in simulation.events.
• test_simulate_events_empty_on_heuristic_fallback — uses the existing test_app() (RPC unreachable) and asserts simulation.events is present but empty.

I do not have a local Rust toolchain, so I could not run cargo test myself — please run the test suite before merging. The diff is mechanical: an events field threaded through four files plus two self-contained tests.

Closes

#1162