/// The number of threads used to process RPC requests and responses.
///
/// Zebra's RPC server has a separate thread pool and a `tokio` executor for each thread.
/// State queries are run concurrently using the shared thread pool controlled by
/// the [`SyncSection.parallel_cpu_threads`](https://doc.zebra.zfnd.org/zebrad/config/struct.SyncSection.html#structfield.parallel_cpu_threads) config.
///
/// We recommend setting both configs to `0` (automatic scaling) for the best performance.
/// This uses one thread per available CPU core.
///
/// Set to `1` by default, which runs all RPC queries on a single thread, and detects RPC
/// port conflicts from multiple Zebra or `zcashd` instances.
///
/// For details, see [the `jsonrpc_http_server` documentation](https://docs.rs/jsonrpc-http-server/latest/jsonrpc_http_server/struct.ServerBuilder.html#method.threads).
///
/// ## Warning
///
/// Changing this config disables RPC port conflict detection.
/// This can allow multiple Zebra instances to share the same RPC port.
///
/// If some of those instances are outdated or failed, RPC queries can be slow or inconsistent.