Performance improvement: Do we need to render building twice?

[matkoniecz]

Currently we render both base buildings (colour affected by dark/light style) and the same buildings are again rendered in style of given layer.

Maybe it would be more efficient to render them once?

https://colouring.london/tiles/base_night/18/130974/87151.png
https://colouring.london/tiles/date_year/18/130974/87151.png

How this can be done:

(1) have the same colour for building with no data both in dark and light style - may be not acceptable

(2) have separate dark and light style for each map style - additional work

Benefit of changes should be increased performance.
This can be tested to check what is the benefit and is it worth extra complexity.