Function cqrs_command_handler 

pub fn cqrs_command_handler<TCommand, TEvent>(
    command_type: impl Into<String>,
    handle: impl Fn(&CqrsCommand<TCommand>) -> Vec<CqrsEventDraft<TEvent>> + 'static,
) -> CqrsCommandHandlerDefinition<TCommand, TEvent>

Creates or computes cqrs_command_handler.