Make sse.PatchElement* sugars more generic

[michaeldebetaz]

This PR add generic functions PatchElementRenderer (for Gostar or Gomponent) and PatchElementRendererWithContext (for Templ). Original PatchElementTempl and PatchElementGostar are kept but defined as convenience wrappers of those generic functions.

This allows to have more generic functions while keeping wrappers for named libraries which come and go.

Example for Templ:

// PatchElementRendererWithContext is a convenience adaptor of [sse.PatchElements] for [ElementRendererWithContext].
func (sse *ServerSentEventGenerator) PatchElementRendererWithContext(r ElementRendererWithContext, opts ...PatchElementOption) error {
	buf := bytebufferpool.Get()
	defer bytebufferpool.Put(buf)
	if err := r.Render(sse.Context(), buf); err != nil {
		return fmt.Errorf("failed to render element: %w", err)
	}
	if err := sse.PatchElements(buf.String(), opts...); err != nil {
		return fmt.Errorf("failed to patch element: %w", err)
	}
	return nil
}

// PatchElementTempl is a convenience adaptor of [sse.PatchElements] for [Templ] components.
//
// [Templ]: https://templ.guide/
func (sse *ServerSentEventGenerator) PatchElementTempl(r ElementRendererWithContext, opts ...PatchElementOption) error {
	return sse.PatchElementRendererWithContext(r, opts...)
}