re_renderer temp & staging allocator for buffers

[Wumpf]

there's an increasing amount of TODO notes in the re_renderer code that want some sort of frame-lived stack allocator for buffers as well as a staging belt for writing data. Given that we always know if something is long or frame lived we can do some pretty cool optimizations

On top of that this would prevent alignment issues we have with uniform buffers now occassionally, see e.g. 3dbc500