Function spawn 

pub async fn spawn(
    config: ServerConfig,
    workspace_root: PathBuf,
    logger: LspLogger,
    apply_edit_bus: Option<ApplyEditBus>,
    configuration_bus: Option<ConfigurationBus>,
    show_document_bus: Option<ShowDocumentBus>,
    show_message_request_bus: Option<ShowMessageRequestBus>,
    event_bus: Option<Arc<EventBus>>,
) -> LspResult<ServerHandle>

Spawn a language server from a ServerConfig.

Performs the initialize handshake before returning. Failures at any handshake step (spawn, framing, decode, server error response, missing required capability) surface as LspError. logger is the shared subsystem logger – in production every server uses the App’s clone; tests pass a fresh LspLogger::with_defaults().