use the render_to_stream API to render a component to a stream of strings.
This works very nicely with the axum-framework making it easy to implement
natively streaming server-side rendering.
render_to_string takes a bloom-core Element and a spawner and returns a string.
Prefer using render_to_stream where possible to get the advantages of streaming rendering.
This function is useful for testing and other use-cases where you need the full string at once,
e.G. if the necessary headers cannot be sent before the full body is rendered.