* Pass Go context down to Renderers
This is useful for cancellation or tracing.
* Add tracing spans to app
Also log things like number of nodes in Map, total number of reports.
instead of a Map, since it's not really a map as it just updates the
given node.
This is more efficient and also matches what we do in similar
situations elsewhere, e.g. in ContainerWithImageNameRenderer and
ProcessWithContainerNameRenderer.
